CSMC 412
Operating Systems
Prof. Ashok K Agrawala
© 2006 Ashok Agrawala
Set 11
Operating System Concepts
11.1
File System Implementation
„ File-System Structure
„ File-System Implementation
„ Directory Implementation
„ Allocation Methods
„ Free-Space Management
„ Efficiency and Performance
„ Recovery
„ Log-Structured File Systems
„ NFS
„ Example: WAFL File System
Operating System Concepts
11.2
1
Objectives
„ To describe the details of implementing local file systems and
directory structures
„ To describe the implementation of remote file systems
„ To discuss block allocation and free-block algorithms and trade-offs
Operating System Concepts
11.3
File System Structure
„ Primary device for File System – Disks
z
Direct Access
z
Written in place
Operating System Concepts
11.4
2
File-System Structure
„ File structure
z
Logical storage unit
z
Collection of related information
„ File system resides on secondary storage (disks)
z
Direct Access
z
Written in place
„ File system organized into layers
„ File control block – storage structure consisting of information
about a file
Operating System Concepts
11.5
Layered File System
Operating System Concepts
11.6
3
File System Implementation
„ Several disk and in memory structures are used to support
the file system
„ On disk the file system contains a variety of information
z
Boot information
z
Disk information – No of blocks
z
Directory Structure
z
Free blocks
z
Files – their data
Operating System Concepts
11.7
File System Implementation
„ Boot Control Block – per volume
Information to boot the OS – typically the first block of the disk.
Boot Block in UFS
Partition Boot Sector in NTFS
„ Volume Control Block – per volume
z Contains volume or partition details
No of blocks. Size of clocks, free block count, free-block
pointers, free FCB count
Super Block in UFS
Stored in Master File table in NTFS
„ Directory Structure – per file system
z In UFS – INODE number and File name
z In NTFS – Master File Table
„ File Control Block – per file
z
Operating System Concepts
11.8
4
A Typical File Control Block
Operating System Concepts
11.9
In Memory Information
„ Mount Table
„ Directory Structure cache
z
Information about recently accessed directories
„ System-wide Open-file Table
z
Copy of FCB of all open files
z
Additional information
„ Per-process open-file Table
z
Pointers into System-wide Open File Table.
Operating System Concepts
11.10
5
In-Memory File System Structures
Operating System Concepts
11.11
File Operations
„ Creating a file
z
Calls logical file system – knows the format of the directory
z
Allocates/creates an FCB
z
Reads the directory into memory
z
Updates it with the new file information
z
Writes back to the disk
„ Opening a file
z
Call passes a file name
z
Search System-Wide Open File Table to see if it is open
If
there – create a per-process entry and point to it
z
Search directory structure for the file name
z
Copy FCB into System-Wide open file table
z
Returns a pointer to per-process table entry
Make
Operating System Concepts
an entry in per-process open file table
11.12
6
File Operations
„ Read and Write Operations
z
Use process open file table entry which also has the pointer
z
This entry is called File Descriptor in UFS and File Handle in
Windows
„ Close
z
Remove process table entry
z
Decrease the open count in the System-wide table. If zero,
write back any updated meta data to disk and remove the
entry.
„ Caching of information – done for efficiency
Operating System Concepts
11.13
Partitions and Mounting
„ Partitions or volumes
z
Divide one disk to look like multiple disks
z
Manage by having a partition table
z
Each partition is treated as a raw disk
z
Root partition
dual
boot
Contains
the OS kernel and other system files
Mounted
at Boot time
Other
z
volumes can be mounted if desired
In Memory Mount Table
Operating System Concepts
11.14
7
Virtual File Systems
„ Virtual File Systems (VFS) provide an object-oriented way of
implementing file systems.
„ VFS allows the same system call interface (the API) to be used for
different types of file systems.
„ The API is to the VFS interface, rather than any specific type of file
system.
Operating System Concepts
11.15
Schematic View of Virtual File System
Operating System Concepts
11.16
8
Directory Implementation
„ Linear list of file names with pointer to the data blocks.
z
simple to program
z
time-consuming to execute
„ Hash Table – linear list with hash data structure.
z
decreases directory search time
z
collisions – situations where two file names hash to the same
location
z
fixed size
Operating System Concepts
11.17
Allocation Methods
„ An allocation method refers to how disk blocks are allocated for
files:
„ Contiguous allocation
„ Linked allocation
„ Indexed allocation
Operating System Concepts
11.18
9
Contiguous Allocation
„ Each file occupies a set of contiguous blocks on the disk
„ Simple – only starting location (block #) and length (number
of blocks) are required
„ Random access
„ Wasteful of space (dynamic storage-allocation problem)
„ Files cannot grow
Operating System Concepts
11.19
Contiguous Allocation
„ Mapping from logical to physical
Q
LA/512
R
Block to be accessed = Q + starting address
Displacement into block = R
Operating System Concepts
11.20
10
Contiguous Allocation of Disk Space
Operating System Concepts
11.21
Extent-Based Systems
„ Many newer file systems (I.e. Veritas File System) use a modified
contiguous allocation scheme
„ Extent-based file systems allocate disk blocks in extents
„ An extent is a contiguous block of disks
z
Extents are allocated for file allocation
z
A file consists of one or more extents.
Operating System Concepts
11.22
11
Linked Allocation
„ Each file is a linked list of disk blocks: blocks may be scattered
anywhere on the disk.
block
=
Operating System Concepts
pointer
11.23
Linked Allocation (Cont.)
„ Simple – need only starting address
„ Free-space management system – no waste of space
„ No random access
„ Mapping
Q
LA/511
R
Block to be accessed is the Qth block in the linked chain of
blocks representing the file.
Displacement into block = R + 1
File-allocation table (FAT) – disk-space allocation used by MS-DOS
and OS/2.
Operating System Concepts
11.24
12
Linked Allocation
Operating System Concepts
11.25
File-Allocation Table
Operating System Concepts
11.26
13
Indexed Allocation
„ Brings all pointers together into the index block.
„ Logical view.
index table
Operating System Concepts
11.27
Example of Indexed Allocation
Operating System Concepts
11.28
14
Indexed Allocation (Cont.)
„ Need index table
„ Random access
„ Dynamic access without external fragmentation, but have
overhead of index block.
„ Mapping from logical to physical in a file of maximum size
of 256K words and block size of 512 words. We need only
1 block for index table.
Q
LA/512
R
Q = displacement into index table
R = displacement into block
Operating System Concepts
11.29
Indexed Allocation – Mapping (Cont.)
„ Mapping from logical to physical in a file of unbounded
length (block size of 512 words).
„ Linked scheme – Link blocks of index table (no limit on
size).
Q1
LA / (512 x 511)
R1
Q1 = block of index table
R1 is used as follows:
Q2
R1 / 512
R2
Q2 = displacement into block of index table
R2 displacement into block of file:
Operating System Concepts
11.30
15
Indexed Allocation – Mapping (Cont.)
„ Two-level index (maximum file size is 5123)
Q1
LA / (512 x 512)
R1
Q1 = displacement into outer-index
R1 is used as follows:
Q2
R1 / 512
R2
Q2 = displacement into block of index table
R2 displacement into block of file:
Operating System Concepts
11.31
Indexed Allocation – Mapping (Cont.)
#
outer-index
index table
Operating System Concepts
file
11.32
16
Combined Scheme: UNIX (4K bytes per block)
Operating System Concepts
11.33
Free-Space Management
„ Bit vector (n blocks)
0 1
2
n-1
…
bit[i] =
0 ⇒ block[i] free
1 ⇒ block[i] occupied
Block number calculation
(number of bits per word) *
(number of 0-value words) +
offset of first 1 bit
Operating System Concepts
11.34
17
Free-Space Management (Cont.)
„ Bit map requires extra space
z
Example:
block size = 212 bytes
disk size = 230 bytes (1 gigabyte)
n = 230/212 = 218 bits (or 32K bytes)
„ Easy to get contiguous files
„ Linked list (free list)
z
Cannot get contiguous space easily
z
No waste of space
„ Grouping
„ Counting
Operating System Concepts
11.35
Free-Space Management (Cont.)
„ Need to protect:
z
Pointer to free list
z
Bit map
Must
be kept on disk
Copy
in memory and disk may differ
Cannot
allow for block[i] to have a situation where
bit[i] = 1 in memory and bit[i] = 0 on disk
z
Solution:
Set
bit[i] = 1 in disk
Allocate
Set
Operating System Concepts
block[i]
bit[i] = 1 in memory
11.36
18
Linked Free Space List on Disk
Operating System Concepts
11.37
Efficiency and Performance
„ Efficiency dependent on:
z
disk allocation and directory algorithms
z
types of data kept in file’s directory entry
„ Performance
z
disk cache – separate section of main memory for frequently
used blocks
z
free-behind and read-ahead – techniques to optimize
sequential access
z
improve PC performance by dedicating section of memory as
virtual disk, or RAM disk
Operating System Concepts
11.38
19
Page Cache
„ A page cache caches pages rather than disk blocks using virtual
memory techniques
„ Memory-mapped I/O uses a page cache
„ Routine I/O through the file system uses the buffer (disk) cache
„ This leads to the following figure
Operating System Concepts
11.39
I/O Without a Unified Buffer Cache
Operating System Concepts
11.40
20
Unified Buffer Cache
„ A unified buffer cache uses the same page cache to cache both
memory-mapped pages and ordinary file system I/O
Operating System Concepts
11.41
I/O Using a Unified Buffer Cache
Operating System Concepts
11.42
21
Various Disk-Caching Locations
Operating System Concepts
11.43
Recovery
„ Consistency checking – compares data in directory structure with
data blocks on disk, and tries to fix inconsistencies
„ Use system programs to back up data from disk to another storage
device (floppy disk, magnetic tape, other magnetic disk, optical)
„ Recover lost file or disk by restoring data from backup
Operating System Concepts
11.44
22
Log Structured File Systems
„ Log structured (or journaling) file systems record each update to
the file system as a transaction
„ All transactions are written to a log
z
A transaction is considered committed once it is written to the
log
z
However, the file system may not yet be updated
„ The transactions in the log are asynchronously written to the file
system
z
When the file system is modified, the transaction is removed
from the log
„ If the file system crashes, all remaining transactions in the log must
still be performed
Operating System Concepts
11.45
UNIX- File System
„ The UNIX file system supports two main objects: files and
directories.
„ Directories are just files with a special format, so the representation
of a file is the basic UNIX concept.
Operating System Concepts
11.46
23
Blocks and Fragments
„ Most of the file system is taken up by data blocks.
„ 4.2BSD uses two block sized for files which have no indirect
blocks:
z
All the blocks of a file are of a large block size (such as 8K),
except the last.
z
The last block is an appropriate multiple of a smaller fragment
size (i.e., 1024) to fill out the file.
z
Thus, a file of size 18,000 bytes would have two 8K blocks and
one 2K fragment (which would not be filled completely).
Operating System Concepts
11.47
Blocks and Fragments (Cont.)
„ The block and fragment sizes are set during file-system creation
according to the intended use of the file system:
z
If many small files are expected, the fragment size should be
small.
z
If repeated transfers of large files are expected, the basic block
size should be large.
„ The maximum block-to-fragment ratio is 8 : 1; the minimum block
size is 4K (typical choices are 4096 : 512 and 8192 : 1024).
Operating System Concepts
11.48
24
Inodes
„
A file is represented by an inode — a record that stores information about a
specific file on the disk.
„
The inode also contains 15 pointer to the disk blocks containing the files’s
data contents.
z
First 12 point to direct blocks.
z
Next three point to indirect blocks
First indirect block pointer is the address of a single indirect block
— an index block containing the addresses of blocks that do
contain data.
Second is a double-indirect-block pointer, the address of a block
that contains the addresses of blocks that contain pointer to the
actual data blocks.
A triple indirect pointer is not needed; files with as many as 232
bytes will use only double indirection.
Operating System Concepts
11.49
Directories
„ The inode type field distinguishes between plain files and
directories.
„ Directory entries are of variable length; each entry contains first the
length of the entry, then the file name and the inode number.
„ The user refers to a file by a path name,whereas the file system
uses the inode as its definition of a file.
z
The kernel has to map the supplied user path name to an inode
z
Directories are used for this mapping.
Operating System Concepts
11.50
25
Directories (Cont.)
„ First determine the starting directory:
If the first character is “/”, the starting directory is the root
directory.
z For any other starting character, the starting directory is the
current directory.
„ The search process continues until the end of the path name is
reached and the desired inode is returned.
„ Once the inode is found, a file structure is allocated to point to the
inode.
„ 4.3BSD improved file system performance by adding a directory
name cache to hold recent directory-to-inode translations.
z
Operating System Concepts
11.51
Mapping of a File Descriptor to an
Inode
„ System calls that refer to open files indicate the file is passing a file
descriptor as an argument.
„ The file descriptor is used by the kernel to index a table of open
files for the current process.
„ Each entry of the table contains a pointer to a file structure.
„ This file structure in turn points to the inode.
„ Since the open file table has a fixed length which is only setable at
boot time, there is a fixed limit on the number of concurrently open
files in a system.
Operating System Concepts
11.52
26
File-System Control Blocks
Operating System Concepts
11.53
Disk Structures
„ The one file system that a user ordinarily sees may actually consist
of several physical file systems, each on a different device.
„ Partitioning a physical device into multiple file systems has several
benefits.
z
Different file systems can support different uses.
z
Reliability is improved
z
Can improve efficiency by varying file-system parameters.
z
Prevents one program form using all available space for a large
file.
z
Speeds up searches on backup tapes and restoring partitions
from tape.
Operating System Concepts
11.54
27
Disk Structures (Cont.)
„ The root file system is always available on a drive.
„ Other file systems may be mounted — i.e., integrated into the
directory hierarchy of the root file system.
„ The following figure illustrates how a directory structure is
partitioned into file systems, which are mapped onto logical
devices, which are partitions of physical devices.
Operating System Concepts
11.55
Mapping File System to Physical
Devices
Operating System Concepts
11.56
28
Implementations
„
The user interface to the file system is simple and well defined,
allowing the implementation of the file system itself to be changed
without significant effect on the user.
For Version 7, the size of inodes doubled, the maximum file and file
system sized increased, and the details of free-list handling and
superblock information changed.
In 4.0BSD, the size of blocks used in the file system was increased
form 512 bytes to 1024 bytes — increased internal fragmentation, but
doubled throughput.
4.2BSD added the Berkeley Fast File System, which increased speed,
and included new features.
z New directory system calls
z truncate calls
z Fast File System found in most implementations of UNIX.
„
„
„
Operating System Concepts
11.57
Layout and Allocation Policy
„ The kernel uses a <logical device number, inode number> pair to
identify a file.
z
The logical device number defines the file system involved.
z
The inodes in the file system are numbered in sequence.
„ 4.3BSD introduced the cylinder group — allows localization of the
blocks in a file.
z
Each cylinder gorup occupies one or more consecutive
cylinders of the disk, so that disk accesses within the cylinder
group require minimal disk head movement.
z
Every cylinder group has a superblock, a cylinder block, an
array of inodes, and some data blocks.
Operating System Concepts
11.58
29
4.3BSD Cylinder Group
Operating System Concepts
11.59
The Sun Network File System (NFS)
„ An implementation and a specification of a software system for
accessing remote files across LANs (or WANs)
„ The implementation is part of the Solaris and SunOS operating
systems running on Sun workstations using an unreliable datagram
protocol (UDP/IP protocol and Ethernet
Operating System Concepts
11.60
30
NFS (Cont.)
„ Interconnected workstations viewed as a set of independent
machines with independent file systems, which allows sharing
among these file systems in a transparent manner
z
A remote directory is mounted over a local file system directory
z
Specification of the remote directory for the mount operation is
nontransparent; the host name of the remote directory has to
be provided
z
The mounted directory looks like an integral subtree of the
local file system, replacing the subtree descending from the
local directory
Files in the remote directory can then be accessed in a
transparent manner
Subject to access-rights accreditation, potentially any file
system (or directory within a file system), can be mounted
remotely on top of any local directory
Operating System Concepts
11.61
NFS (Cont.)
„ NFS is designed to operate in a heterogeneous environment of
different machines, operating systems, and network architectures;
the NFS specifications independent of these media
„ This independence is achieved through the use of RPC primitives
built on top of an External Data Representation (XDR) protocol
used between two implementation-independent interfaces
„ The NFS specification distinguishes between the services provided
by a mount mechanism and the actual remote-file-access services
Operating System Concepts
11.62
31
Three Independent File Systems
Operating System Concepts
11.63
Mounting in NFS
Mounts
Operating System Concepts
Cascading mounts
11.64
32
NFS Mount Protocol
„ Establishes initial logical connection between server and client
„ Mount operation includes name of remote directory to be mounted and
name of server machine storing it
z
Mount request is mapped to corresponding RPC and forwarded to
mount server running on server machine
z
Export list – specifies local file systems that server exports for
mounting, along with names of machines that are permitted to
mount them
„ Following a mount request that conforms to its export list, the server
returns a file handle—a key for further accesses
„ File handle – a file-system identifier, and an inode number to identify
the mounted directory within the exported file system
„ The mount operation changes only the user’s view and does not affect
the server side
Operating System Concepts
11.65
NFS Protocol
„ Provides a set of remote procedure calls for remote file operations.
The procedures support the following operations:
z
searching for a file within a directory
z
reading a set of directory entries
z
manipulating links and directories
z
accessing file attributes
z
reading and writing files
„ NFS servers are stateless; each request has to provide a full set of
arguments
(NFS V4 is just coming available – very different, stateful)
„ Modified data must be committed to the server’s disk before results
are returned to the client (lose advantages of caching)
„ The NFS protocol does not provide concurrency-control
mechanisms
Operating System Concepts
11.66
33
Three Major Layers of NFS Architecture
„ UNIX file-system interface (based on the open, read, write, and
close calls, and file descriptors)
„ Virtual File System (VFS) layer – distinguishes local files from
remote ones, and local files are further distinguished according to
their file-system types
z
The VFS activates file-system-specific operations to handle
local requests according to their file-system types
z
Calls the NFS protocol procedures for remote requests
„ NFS service layer – bottom layer of the architecture
z
Implements the NFS protocol
Operating System Concepts
11.67
Schematic View of NFS Architecture
Operating System Concepts
11.68
34
NFS Path-Name Translation
„ Performed by breaking the path into component names and
performing a separate NFS lookup call for every pair of component
name and directory vnode
„ To make lookup faster, a directory name lookup cache on the
client’s side holds the vnodes for remote directory names
Operating System Concepts
11.69
NFS Remote Operations
„ Nearly one-to-one correspondence between regular UNIX system
calls and the NFS protocol RPCs (except opening and closing files)
„ NFS adheres to the remote-service paradigm, but employs
buffering and caching techniques for the sake of performance
„ File-blocks cache – when a file is opened, the kernel checks with
the remote server whether to fetch or revalidate the cached
attributes
z
Cached file blocks are used only if the corresponding cached
attributes are up to date
„ File-attribute cache – the attribute cache is updated whenever new
attributes arrive from the server
„ Clients do not free delayed-write blocks until the server confirms
that the data have been written to disk
Operating System Concepts
11.70
35
Example: WAFL File System
„ Used on Network Appliance “Filers” – distributed file system
appliances
„ “Write-anywhere file layout”
„ Serves up NFS, CIFS, http, ftp
„ Random I/O optimized, write optimized
z
NVRAM for write caching
„ Similar to Berkeley Fast File System, with extensive modifications
Operating System Concepts
11.71
The WAFL File Layout
Operating System Concepts
11.72
36
Snapshots in WAFL
Operating System Concepts
11.73
NTFS
„ File Systems supported by Windows
„ NTFS Design Goals
„ File System Driver Architecture
„ NTFS Operation
„ Windows File System On-Disk Structure
„ NTFS File Compression
Operating System Concepts
11.74
37
Windows File System - Terminology
„
Sectors:
z
z
„
File system formats:
z
z
„
Define the way data is stored on storage media
Impact a file system features: permissions & security, limitations on file size, support for small/large
files/disks
Clusters:
z
z
z
„
hardware-addressable blocks on a storage medium
Typical sector size on hard disks for x86-based systems is 512 bytes
Addressable blocks that many file system formats use
Cluster size is always a multiple of the sector size
Cluster size tradeoff: space efficiency vs. access speed
Metadata:
z
Data stored on a volume in support of file system format management
z
Metadata includes the data that defines the placement of files and directories on a volume,
for example
z
Typically not accessible to applications
Operating System Concepts
11.75
Formats Supported by Windows
„ CD-ROM File System (CDFS)
„ Universal Disk Format (UDF)
„ File Allocation Table (FAT12, FAT16, and FAT32)
„ New Technology File System (NTFS)
Operating System Concepts
11.76
38
CDFS
„
CDFS, or, is a relatively simple format that was defined in 1988 as the read-only
formatting standard for CD-ROM media.
„
Windows 2000 implements ISO 9660-compliant CDFS in
\Winnt\System32\Drivers\Cdfs.sys, with long filename support defined by Level 2 of the
ISO 9660 standard
„
Because of its simplicity, the CDFS format has a number of restrictions
„
z
Directory and file names must be fewer than 32 characters long
z
Directory trees can be no more than eight levels deep
CDFS is considered a legacy format because the industry has adopted the Universal
Disk Format (UDF) as the standard for read-only media
Operating System Concepts
11.77
UDF
„
OSTA (Optical Storage Technology Association) defined UDF in 1995 as a
format to replace CDFS for magneto-optical storage media, mainly DVDROM
z
„
„
The Windows 2000 UDF file system implementation is ISO 13346compliant and supports UDF versions 1.02 and 1.5
UDF file systems have the following traits:
z
Filenames can be 255 characters long
z
The maximum path length is 1023 characters
Although the UDF format was designed with rewritable media in mind, the
Windows 2000 UDF driver (\Winnt\System32\Drivers\Udfs.sys) provides
read-only support
Operating System Concepts
11.78
39
FAT
„
FAT (File Allocation Table) file systems are a legacy format that originated in DOS and
Windows 9x
„
Reasons why Windows supports FAT file systems:
z
to enable upgrades from other versions of Windows
z
compatibility with other operating systems in multiboot systems
z
as a floppy disk format
„
Windows FAT file system driver is implemented in \Winnt\System32\Drivers\Fastfat.sys
„
Each FAT format includes a number that indicates the number of bits the format uses
to identify clusters on a disk
Boot sector
File allocation
table 1
File allocation
table 2 (duplicate)
Root directory Other directories and all files
FAT format organization
Operating System Concepts
11.79
FAT12
„ FAT12's 12-bit cluster identifier limits a partition to storing a
maximum of 212 (4096) clusters
z
Windows uses cluster sizes from 512 bytes to 8 KB in size,
which limits a FAT12 volume size to 32 MB
z
Windows uses FAT12 as the format for all 5-inch floppy disks
and 3.5-inch floppy disks, which store up to 1.44 MB of data
Operating System Concepts
11.80
40
FAT16
„ FAT16, with a 16-bit cluster identifier, can address 216 (65,536)
clusters
z
On Windows, FAT16 cluster sizes range from 512 bytes (the
sector size) to 64 KB, which limits FAT16 volume sizes to 4 GB
z
The cluster size Windows uses depends on the size of a
volume
Operating System Concepts
11.81
FAT32
„ FAT32 is the most recently defined FAT-based file system format
z
it's included with Windows 95 OSR2, Windows 98, and Windows Millennium
Edition
„ FAT32 uses 32-bit cluster identifiers but reserves the high 4 bits, so in effect it has 28bit cluster identifiers
z Because FAT32 cluster sizes can be as large as 32 KB, FAT32 has a theoretical
ability to address 8 TB volumes
z Although Windows works with existing FAT32 volumes of larger sizes (created in
other operating systems), it limits new FAT32 volumes to a maximum of 32 GB
z FAT32's higher potential cluster numbers let it more efficiently manage disks than
FAT16; it can handle up to 128-MB volumes with 512-byte clusters
„ Unlike FAT12 and FAT16, root directory is not fixed size or location
z Largest file size on Windows is 4GB (largest on Win9x is 2G)
Operating System Concepts
11.82
41
NTFS
„
NTFS is the native file system format of Windows
„
NTFS uses 64-bit cluster indexes
„
z
Theoretical ability to address volumes of up to 16 exabytes (16 billion GB)
z
Windows 2000 limits the size of an NTFS volume to that addressable with 32-bit
clusters, which is 128 TB (using 64-KB clusters)
Why use NTFS instead of FAT? FAT is simpler, making it faster for some operations,
but NTFS supports:
z
Larger file sizes and disks
z
Better performance on large disks, large directories, and small files
z
Reliability
z
Security
Operating System Concepts
11.83
CIFS –
the Common Internet File System
„
„
„
„
The standard Windows network file system
The file sharing protocol at the heart of CIFS is an updated version of the Server Message Block (SMB) protocol
z
dates back to the mid-1980s
z
in 1996/97, Microsoft submitted draft CIFS specifications to the IETF
The SMB protocol was originally developed to run over NetBIOS (Network Basic Input Output System) LANs
z
Until Windows 2000, NetBIOS support was required for SMB transport
z
The machine and service names visible in the Windows Network Neighborhood are, basically, NetBIOS
addresses (Windows 2000 and later use DNS names)
Windows 3.11 (WfW) introduced:
z
service announcement and location system called Browsing
z
The browser service provides the list of available file and print services presented in the Network
Neighborhood
z
Workgroup concept was expanded to create NT Domains
Operating System Concepts
11.84
42
File System Format Compatibility
„ FAT12/FAT16 supported on all Microsoft OS’s
„ FAT32:
z
Only Windows 2000/XP/2003
z
Winternals FAT32 driver for NT4
„ NTFS:
z
Only Windows NT-based OS’s
z
Winternals NTFSDOS for DOS access
z
Winternals NTFS for Windows 98 for Win9x/Me
Operating System Concepts
11.85
NTFS Design Goals
„
Overcome limitations inherent in FAT / HPFS
z
FAT (File Allocation Table) does not support large disks very well
z
FAT16 (MS-DOS file system) supports only up to 216 clusters
and 2 GB disks (with 64 Kb clusters!!)
z
FAT / root directory represents single point of failure
z
Number of entries in root directory is limited
z
HPFS removed some of FAT‘s limitations, but still did not support
recoverability, security, data redundancy, and fault-tolerance
(later versions of HPFS support up to 2TeraByte disks)
Operating System Concepts
11.86
43
NTFS Recoverability
PC disk I/O in the old days: Speed was most important
NTFS changes this view – Reliability counts most:
„ I/O operations that alter NTFS structure are implemented as atomic transactions
z Change directory structure,
z extend files, allocate space for new files
„ Transactions are either completed or rolled back
„ NTFS uses redundant storage for vital FS information
z Contrasts with FAT / HPFS on-disk structures, which have single sectors
containing critical file system data
z Read error in these sectors -> volume lost
Operating System Concepts
11.87
NTFS Security and Recoverability
NTFS security is derived from Windows object model
„
Open file is implemented as file object;
security descriptor is stored on disk as part of the file
„
NT security system verifies access rights when a process tries to open a handle to any object
„
Administrator or file owner may set permissions
NTFS recoverability ensures integrity of FS structure
„
No guarantees for complete recovery of user files
„
Layered driver model + FTDISK driver
z
z
Mirroring of data – RAID level 1
Striping of data - RAID level 5 (one disk with parity info)
Operating System Concepts
11.88
44
Large Disks and Large Files
„
Efficient support for large files and disks in NTFS
FAT16:
„
z
16-bit wide table stores allocation status of disk
Up to 65.536 clusters per volume (#files !!); adjustable cluster size
z
„
FAT32:
z
New in since Windows 2000
4kb clusters on volumes up to 8 GB
Can relocate root directory / use backup copy of FAT
Root directory is ordinary cluster chain – no limits on #entries
z
z
z
„
HPFS (support dropped in NT 4.0):
z
32 bits to enumerate allocation units; maximum file size: 4GB
Allocates disk space in terms of physical sectors of 512 bytes;
problem with some disks (1024 bit sectors)
z
Operating System Concepts
11.89
Large Disks and Large Files (contd.)
„
„
„
„
NTFS enumerates cluster with 64-bit numbers
Up to 264 clusters of up to 64 Kbytes size
Maximum file size: 264 bytes
Cluster size is adjustable
z
z
„
512 bytes on small disks
Maximum of 64Kb on large disks
Multiple data streams
z
z
z
z
z
File info: name, owner, time stamps, type implemented as attribute
Each attribute consists of a stream – sequence of bytes
Default data stream has no name
Used to implement
services for Macintosh
in Windows NT Server
New streams can be added: myfile.dat:stream2
File operations manipulate all streams simultaneously
Operating System Concepts
11.90
45
Other NTFS Features
„
Multiple data streams
„
Unicode-based names
„
Hard links
„
Junctions
„
Compression and sparse files
„
Change logging
„
Per-user volume quotas
„
Link tracking
„
Encryption
„
POSIX support
„
Defragmentation
Operating System Concepts
11.91
Multiple Data Streams
„
In NTFS, each unit of information associated with a file, including its name,
its owner, its time stamps, its contents, and so on, is implemented as a file
attribute (NTFS object attribute)
„
Each attribute consists of a single stream, that is, a simple sequence of
bytes
z
This generic implementation makes it easy to add more attributes (and
therefore more streams) to a file
z
Because a file's data is "just another attribute" of the file and because
new attributes can be added, NTFS files (and file directories) can
contain multiple data streams
Operating System Concepts
11.92
46
Multiple Data Streams
„
An NTFS file has one default data stream, which has no name
z
An application can create additional, named data streams and access
them by referring to their names.
z
To avoid altering the Microsoft Windows I/O APIs, which take a string
as a filename argument, the name of the data stream is specified by
appending a colon (:) to the filename e.g. myfile:stream2
Operating System Concepts
11.93
Unicode Names
„ Like Windows as a whole, NTFS is fully Unicode enabled, using
Unicode characters to store names of files, directories, and
volumes
Operating System Concepts
11.94
47
Hard Links
„
A hard link allows multiple paths to refer to the same file or directory
z
If you create a hard link named C:\Users\Documents\Spec.doc that refers to the
existing file C:\My Documents\Spec.doc, the two paths link to the same on-disk
file and you can make changes to the file using either path
z
can create hard links
with the Windoqs API
CreateHardLink function
or the ln POSIX function
Operating System Concepts
11.95
Junctions
„ Junctions, also called symbolic links, allow a directory to redirect
file or directory pathname translation to an alternate directory
z
If the path C:\Drivers is a junction that redirects to
C:\Winnt\System32\Drivers, an application reading
C:\Drivers\Ntfs.sys actually reads
C:\Winnt\System\Drivers\Ntfs.sys
z
Junctions are a useful way to lift directories that are deep in a
directory tree to a more convenient depth without disturbing the
original tree's structure or contents
Operating System Concepts
11.96
48
Junctions
„ You can create junctions with the junction tool from Sysinternals or
the linkd tool from the Resource Kits
Operating System Concepts
11.97
Change Logging
„ Many types of applications, such as incremental backup utilities,
need to monitor a volume for changes
„ An obvious way to watch for changes is to perform a full scan
z
Very performance inefficient
„ There is a way for an application to “wait” on a directory and be told
of notifications
z
An application can miss changes since it must specify a buffer
to hold them
Operating System Concepts
11.98
49
Change Logging
„
With Windows 2000, NTFS introduces the change log,
which is a sparse metadata file that records file system
events (not enabled by default)
z
As the file exceeds its maximum on-disk size,
NTFS frees the disk space for the oldest portions
marking them empty
z
An application uses Win32 APIs to read events
z
The log file is shared, and generally large enough
that an application won’t miss changes even
during heavy file system activity
Operating System Concepts
11.99
Per-User Volume Quotas
„
„
NTFS quota-management support allows for per-user specification of quota
enforcement
z
Can be configured to log an event indicating the occurrence to the
system Event Log if a user surpasses his warning limit
z
If a user attempts to use more volume storage then her quota limit
permits, NTFS can log an event to the system Event Log and fail the
application file I/O that would have caused the quota violation with a
"disk full" error code
User disk space is tracked on a per-volume basis by summing the logical
sizes of all the files and directories that have the user as the owner in their
security descriptors
Operating System Concepts
11.100
50
Link Tracking
„
Several types of symbolic file links are used by layered applications
z
Shell shortcuts allow users to place files in their shell namespace (on their
desktop, for example) that link to files located in the file system namespace
z
Object linking and embedding (OLE) links allow documents from one application
to be transparently embedded in the documents of other applications
„
In the past, these links were difficult to manage
„
Windows now has a link-tracking service, TrkWks (it runs in services.exe), tags link
sources with a unique object ID
z
If someone moved a link source (what a link points to), the link broke
z
NTFS can return the name of a file given a link, so if the link moves the service
can query each of a system’s volume for the object ID
z
A distributed link-tracking service, TrkSvr, works to track link source movement
across systems
Operating System Concepts
11.101
Encryption
„
„
„
While NTFS implements security for files and directories, the security is ineffective if
the physical security of the computer is compromised
z
Can install a parallel copy of Windows
z
NTFSDOS
Encrypting File System (EFS)
z
Like compression, its operation is transparent
z
Also like compression, encryption is a file and directory attribute
z
Files that are encrypted can be accessed only by using the private key of an
account's EFS private/public key pair, and private keys are locked using an
account's password
While you might think that its implemented as a file system filter driver, it’s a driver
that’s tightly connected to NTFS
Operating System Concepts
11.102
51
POSIX Support
„ POSIX support requires two file system features:
z
Primary group in security descriptor
z
Case-sensitive names
Operating System Concepts
11.103
Defragmentation
„ Fragmentation: A file is fragmented if its data occupies
discontiguous clusters
Operating System Concepts
11.104
52
Defragmentation
„
A common myth is that NTFS doesn’t fragment, but it does
z
Defragmentation APIs have been present since NT 4
z
Windows 2000 introduced a non-schedulable graphical defragmenter
z
A command line interface was added in Windows XP
Operating System Concepts
11.105
Compression and Sparse Files
„
„
NTFS supports transparent compression of files
z
When a directories is marked compressed it means any files or
subdirectories are marked compressed
z
Compression is performed on 16-cluster blocks of a file
z
Use Explorer or the compact tool to compress files (compact shows
compression rations for compressed files)
Sparse files are an application-controlled form of compression that define
parts of a file as empty – those areas don’t occupy any disk space
z
Applications use Windows APIs to define empty areas
Operating System Concepts
11.106
53
NTFS File System Driver
Flush the
log file
Log file
service
Write the
cache
Cache
manager
Access the mapped
file or flush the cache
Log the transaction
Read/write the file
I/O manager
NTFS driver
Fault tolerant
driver
Load data
from disk
into
memory
Disk driver
Read/write
a mirrored
or striped
volume
Read/write
the disk
Virtual memory
manager
Operating System Concepts
11.107
Components related to NTFS
Cache Manager
„
„
System wide caching
z for NTFS and other file systems drivers
z Including network file system drivers (server and redirectors)
Cached files are mapped into virtual memory
z Specialized interface from Cache Manager to NT virtual memory manager
z Memory manager calls NTFS to access disk driver and obtain file
Log File Service
z
z
z
2 copies of transaction logs
Transaction log is flushed to disk before write-data is sent to disk
Cache manager performs actual flush operation
Operating System Concepts
11.108
54
NTFS & File Objects
Process
Handle table
File object
Object
manager
data
structures
File object
File
control
block
Data
attribute
NTFS data
structures
App accesses files as
NT objects by handles.
Object Manager and security
subsystem verify access rights
Operating System Concepts
Stream
control
blocks
Master file
table
Userdefined
attribute
(used to manage
the on-disk
structure)
NTFS
database
(on disk)
11.109
NTFS On-Disk Structure
„
„
„
„
„
Volumes correspond to logical partitions on disk
Fault tolerant volumes may span multiple disks
z Windows 2000 Disk Administrator utility
Volume consists of series of files + unallocated space
z FAT volume: some areas specially formatted for file system
z NTFS volume: all data are stored as ordinary files
NTFS refers internally to clusters
z Cluster factor: #sectors/cluster; varies with volume size;
(integral number of physical sectors; always a power of 2)
Logical Cluster Numbers (LCNs):
z refer to physical location
z LCNs are contiguous enumeration of all clusters on a volume
Operating System Concepts
11.110
55
NTFS Cluster Size
„
„
„
„
Default cluster size is disk-size dependent
z 512 bytes for small disks (up to 512 MB)
z 1 KB for disks up to 1 GB
z 2 KB for disks between 1 and 2 GB
z 4 KB for disks larger than 2 GB
Tradeoff: disk fragmentation versus wasted space
NTFS refers to physical locations via LCNs
z Physical cluster = LCN * cluster-factor
Virtual Cluster Numbers (VCNs):
z Enumerates clusters belonging to a file; mapped to LCNs
z LCNs are not necessarily physically contiguous
Operating System Concepts
11.111
Master File Table
„
All data stored on a volume is contained in a file
MFT: Heart of NTFS volume structure
z Implemented as array of file records
z One row for each file on the volume
(including one row for MFT itself)
z Metadata files store file system structure information
(hidden files; $MFT; $Volume...)
z More than one MFT record for highly fragmented
files
NTFS
z Nfi.exe Utility from OEM Support Tools allows to
metadata
dump MFT content
file
(see support.microsoft.com/support/
kb/articles/Q253/0/66.asp)
MFT
MFT copy (partial)
Log file
Volume file
Attribute def. table
Root directory
Bitmap file
Boot file
Bad cluster file
...
User files and dirs.
Operating System Concepts
11.112
56
NTFS operation
Mounting a volume
NTFS looks in boot file for physical address of MFT ($MFT)
2nd entry in MFT points to copy of MFT ($MFTMirr)
z
used to locate metadata files if MFT is corrupted
MFT entry in MFT contains VCN-to-LCN mapping info
NTFS obtains from MFT addresses of metadata files
z
NTFS opens these files
NTFS performs recovery operations
File system is now ready for user access
1.
2.
3.
4.
5.
6.
Operating System Concepts
11.113
NTFS metadata
„
NTFS writes to log file ($LogFile)
„
Root directory:
z
z
Record all commands that change volume structure
z
When NTFS tries to open a file, it starts search in the root directory
Once the file is found, NTFS stores the file‘s MFT file reference
z
Subsequent read/write ops. may access file‘s MFT record directly
„
Bitmap file ($Bitmap):
„
Boot file ($Boot):
z
z
z
z
stores allocation state volume; each bit represents one cluster
Stores bootstrap code
Has to be located at special disk address
Represented as file by NTFS -> file ops. possible (!) (no editing)
Operating System Concepts
11.114
57
NTFS metadata (contd.)
„ Bad-cluster file ($BadClus)
z
Records bad spots on the disk
„ Volume file ($Volume)
z
Contains: volume name, NTFS version
z
Bit, which indicates whether volume is corrupted
„ Attribute Definition Table ($AttrDef)
z
Defines attribute types supported on the volume
z
Indicates whether they can be indexed, recovered, etc.
Operating System Concepts
11.115
File Records &
File Reference Numbers
Sequence
number
63
„
„
File number
0
47
File on NTFS volume is identified by file reference
z File number == index in MFT
z Sequence number – used by NTFS for consistency checking;
incremented each time a reference is re-used
File Records:
z File is collection of attribute/value pairs (one of which is data)
z Unnamed data attribute
z Other attributes: filename, time stamp, security descriptor,...
z Each file attribute is stored as separate stream of bytes within a file
Operating System Concepts
11.116
58
File Records (contd.)
„
NTFS doesn‘t read/write files:
z It reads/writes attribute streams
z Operations: create, delete, read (byte range), write (byte range)
z Read/write normally operate on unnamed data attribute
Windows optimization: Security descriptors
are stored in a central file and referenced
by each file record (saves disk space)
Master File Table
Standard
information
Security
Filename descriptor
Data
MFT record for a small file
Operating System Concepts
11.117
Standard Attributes for NTFS Files
Attribute
Description
Standard information
File attributes: read-only, archive, etc; time stamps; creation/modification time; hard
link count
Filename
Name in Unicode characters; multiple filename attributes possible (POSIX links!!);
short names for access by MS-DOS and 16-bin Win applications
Security descriptor
Specifies who owns the file and who can access it
data
Contents of the file; a file has one default unnamed data attribute; directory has no
default data attrib.
Index root, index
Three attributes used to implement filename allocation, bitmap index for large
directories (dirs. only)
Attribute list
List of attributes that make up the file and first reference of the MFT record in which
the attribute is located (for files which require multiple MFT file records)
Operating System Concepts
11.118
59
Attributes (contd.)
„
„
„
„
„
Each attribute in a file record has a name and a value
NTFS identifies attributes:
z Uppercase name starting with $: $FILENAME, $DATA
Attribute‘s value: Byte stream
z The filename for $FILENAME
z The data bytes for $DATA
Attribute names correspond to numeric typecodes
File attributes in an MFT record are ordered by typecodes
z Some attribute types may appear more than once (e.g. Filename)
Operating System Concepts
11.119
Filenames
„
„
„
„
POSIX:
z Case-sensitive, trailing periods & spaces
z NTFS namespace equiv. to POSIX space
Win32:
z Long filenames, unicode names
z Multiple dots, embedded spaces, beginning dots
MS-DOS:
z 8.3 names, case does not matter
NTFS generates MS-DOS names for Win32 files automatically
z Fully functional aliases for NTFS names
z Stored in same directory as long names; dir /x
Namespaces
POSIX
subsystem
Win32
subsystem
MS-DOS
Win16 clients
Operating System Concepts
11.120
60
MS-DOS filenames in NTFS
Standard info
NTFS filename
MS-DOS filename
Security desc.
Data
MFT file record with MS-DOS filename attribute
„
NTFS name and MS-DOS name are stored in same file record and refer to same file
z
Renaming changes both filenames
Open, read, write, delete work with both names equally
z
„
POSIX hardlinks are implemented in similar way
„
Generation of MS-DOS names:
z
Deleting a file with multiple names only decreases link count
Remove all illegal chars; remove all but one period; truncate to 6 chars
Append ~1 to name; truncate extension to 3 chars; all uppercase
Increment ~1 if filename duplicates an existing name in directory
1.
2.
3.
Operating System Concepts
11.121
Resident & Nonresident Attributes
„
Small files:
z
All attributes and values fit into MFT
z
Attribute with value in MFT is called „resident“
z
All attributes start with header (always resident)
z
Header contains offset to attr. value and length of value
Standard info
NTFS filename
Security desc.
Data
header
„RESIDENT“
Offset: 8h
Length: 14h
Operating System Concepts
value
MYFILE.DAT
11.122
61
Attributes (contd.)
„ Small directory:
z
index root attribute contains index of file references for files and
subdirectories
Standard info
NTFS filename Security desc.
Index root
Empty
Index of files
file1, file2, file3,...
MFT file record for a small directory
• If file attribute does not fit into MFT:
•
•
•
•
NTFS allocates separate cluster (run, extent) to store the values
NTFS allocates additional runs if an attribute‘s value later grows
Those attributes are called „non-resident“
Header of non-resident attribute contains location info
Operating System Concepts
11.123
Large files & directories
Standard info
NTFS filename Security desc.
Data
HPFS extended attr.
MFT
record
for large
filegrow
with
data
runs
„
Only attributes
that can
can2be
non-resident
„
Filename & standard info are always resident
„
Index of files for directories forms B+ tree
Standard info
NTFS filename Security desc. Index root Index allocation
Bitmap
Index of files
file4, file8
MFT file record for a large directory
with nonresident filename index
file1, file2, file3
Operating System Concepts
VCN-to-LCN
mappings
file5, file6
11.124
62
Large files (contd.)
„
NTFS keeps track of runs by means of VCN
(Virtual Cluster Numbers)
z
z
z
Logical Cluster Numbers represent an entire volume
Virtual Cluster Numbers represent clusters belonging to one file
Attribute lists may extend over multiple runs (not only data)
Standard info
NTFS filename Security desc.
VCN-to-LCN mappings for a
nonresident data attribute
VCN 0
1
2
Data
Starting
VCN
Starting
LCN
Number of
clusters
0
1355
4
4
1588
4
VCN 4
3
Data
6
7
Data
LCN 1355 1356 1357 1358
Operating System Concepts
5
LCN 1588 1589 1590 1591
11.125
Data Compression
„
NTFS supports compression
z
Per-file, per-directory, per-volume basis
z
NTFS compression is performed on user data only,
not NTFS metadata
„
Inspect files/volume via Winndows API:
GetVolumeInformation(), GetCompressedFileSize()
„
Change settings for files/directories:
DeviceIoControl()
with flags
FSCTL_GET_COMPRESSION, FSCTL_SET_COMPRESSION
Operating System Concepts
11.126
63
Compression of sparse files
„
„
NTFS zeroes all file contents on creation (C2 req.)
Many sparse files contain large amount of zero-bytes
z These bytes occupy space on disk – unless files are compressed
Standard info
VCN 0
1
NTFS filename Security desc.
2
3
....
15
Data
Starting
VCN
Starting
LCN
Number of
clusters
0
1355
16
32
1588
16
48
96
16
128
324
16
Data
LCN 1355 1356 1357 1358 ....
VCN 32
33
34
35
...
Data
LCN 1588 1589 1590 1591 ....
Operating System Concepts
1370
47
Certain ranges of VCNs have no
(16-31, 6464-127)
1603 disk allocation (1611.127
Compressing Nonsparse Data
„
„
„
NTFS divides the file‘s unprocessed data into
compression units 16 clusters long
Certain sequence might not compress much
z NTFS determines for each compression unit whether it will shrink
by at least on cluster
z If data does not compress, NTFS allocates cluster space and simply writes data
z If data compresses at least one cluster, NTFS allocates only the clusters needed for
compressed data
When writing data, NTFS ensures that each run begins on virtual 16-cluster boundary
z NTFS reads/writes at least one compression unit when accessing a file
z Read-ahead + asynch. decompression improves performance
Operating System Concepts
11.128
64
Data runs of a compressed file
15
VCN 0
Compressed data
LCN 19
20 21
16
22
31
Compressed data
23
24
25
32
26 27
28
29
30
47
Noncompressed data
97
Starting
VCN
Starting
LCN
No. of
clusters
0
19
4
16
23
8
32
97
16
48
113
10
98 99
48
100 101 102 103 104 105 106 107 108 109 110 111 112
63
Compressed data
113 114 115 116 117 118 119 120 121 122
Operating System Concepts
MFT record for a compressed file
11.129
Windows - NTFS Extensions
„
„
„
„
Disk quotas on per-user bases
Security descriptors (ACLs) can be stored once but referenced in multiple files
Native support for properties (OLE), including indexing
Reparse points – implementation of symbolic links
z
„
„
z
„
„
Mount points for arbitrary file system volumes
Support for sparse files
Distributed link tracking (via global object Ids)
Renaming the target file will no longer break links (shortcuts...)
Add disk space to an NTFS volume without reboot
No decompressing when transmitting files over network
Operating System Concepts
11.130
65
File System Driver Architecture
„
Local File System Drivers (Local FSDs):
z
z
z
z
z
z
Ntfs.sys, Fastfat.sys, Udfs,sys, Cdfs,sys
Responsible for registering with the I/O manager and volume recognition/integrity checks
FSD creates device objects for each mounted file system format
I/O manager makes connection between volume‘s device objects (Created by storage
device) and the FSD‘s device object
Local FSDs use cache manager to improve file access performance
Dismount operation permits the system to disconnect FSD from volume object
When media is changed or when application requires raw device access
I/O manager reinitiated volume mount operation on next access to media
Operating System Concepts
11.131
Layered Drivers I/O System Architecture
Environment
subsystem or
DLL
1) Call I/O service
2)The I/O manager creates an IRP,
initializes first stack location and
calls file system driver
IRP
3)File system driver fills in a 2nd
IRP stack location and calls
the disk driver
7)Return I/O pending status
User mode
Kernel mode
Services
I/O manager
6)Return I/O pending status
File system
driver
IRP
5)Return I/O pending status
Disk
driver
4)Send IRP data to device
(or queue IRP), and return
Operating System Concepts
Optimization: associated IRPs
may work in parallel on a single
I/O request
11.132
66
File System Driver Architecture (contd.)
Remote File System Drivers (Remote FSDs):
„
Client-side FSD translates I/O requests from applications into network file system protocol
commands
„
Server-side FSD listens for network commands and issues I/O requests to local FSD
„
Windows client-side remote FSD: LANMan Redirector
z
z
„
z
user mode
kernel mode
I/O manager
Implemented as port/miniport driver
Includes Windows service Workstation
Server-side FSD server: LANMan Server
z
Application
Includes Windows service Server
CIFS – common internet file system (enhancement of Server
Message Block protocol)
Remote FSD
(redirector)
server
client
Remote FSD
(server)
Local FSD
volume
Operating System Concepts
Storage device
driver
11.133
Windows Remote File Drivers:
Server Message Block (SMB) protocol
„
SMB is a client server,
request-response protocol.
Addl. info at
http://anu.samba.org/
cifs/docs/what-is-smb.html
„
The only exception to the request-response nature of SMB
is when the client has requested opportunistic locks (oplocks) and the server subsequently has
to break an already granted oplock because another client has requested a file open with a
mode that is incompatible with the granted oplock.
„
In this case, the server sends an unsolicited message to the client signaling the oplock break.
Operating System Concepts
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67
SMB and the OSI model
„
„
Clients connect to servers using TCP/IP (actually NetBIOS over TCP/IP as specified in RFC1001
and RFC1002), NetBEUI or IPX/SPX.
SMB was also sent over the DECnet protocol.
Digital (now HP) did this for their PATHWORKS product
Operating System Concepts
11.135
SMB characteristics
„
NetBIOS Names
z
If SMB is used over TCP/IP, DECnet or NetBEUI, then NetBIOS names must be used in a number of
cases.
z
NetBIOS names are up to 15 characters long, and are usually the name of the computer that is running
NetBIOS.
z
Microsoft, and some other implementers, insist that NetBIOS names be in upper case, especially when
presented to servers as the CALLED NAME.
„
Protocol functionality (Core protocol):
z
connecting to and disconnecting from file and print shares
z
opening and closing files
z
opening and closing print files
z
reading and writing files
z
creating and deleting files and directories
z
searching directories
z
getting and setting file attributes
z
Locking and unlocking byte ranges in files
Operating System Concepts
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68
SMB characteristics (contd.)
Security
„
„
„
The SMB model defines two levels of security:
Share level.
z Each share can have a password, and a client only needs that password to access all files
under that share.
z This was the first security model that SMB had and is the only security model available in the
Core and CorePlus protocols.
User Level.
z Protection is applied to individual files in each share and is based on user access rights.
z Each user (client) must log in to the server and be authenticated by the server.
z
When it is authenticated, the client is given a UID which it must present on all subsequent
accesses to the server.
z This model has been available since LAN Manager 1.0.
Operating System Concepts
11.137
SMB Clients and Servers
„
„
Clients:
z Included in WfW 3.x, Win 95, Win98, Win ME and Windows NT/2000/XP/Server
2003/Vista.
z smbclient from Samba, smbfs for Linux, SMBlib
Servers:
z Microsoft Windows for Workgroups 3.x, Win95, Win98, Win ME, Windows
NT/2000/XP/Server 2003/Vista
z Samba (Linux, Solaris, SunOS, HP-UX, ULTRIX, DEC OSF/1, Digital UNIX, Dynix
(Sequent), IRIX (SGI), SCO Open Server, DG-UX, UNIXWARE, AIX, BSDI, NetBSD,
NEXTSTEP, A/UX)
z The PATHWORKS family of servers from Digital
z LAN Manager for OS/2, SCO, etc
z VisionFS from SCO
z Advanced Server for UNIX from AT&T (NCR?)
z LAN Server for OS/2 from IBM
Operating System Concepts
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69