DB2 on z/OS and Single Round-Trip J0 with
Performance Enhancements in
EMC Enginuity 5772+
Applied Technology
Abstract
This white paper describes the enhancement to DB2 on z/OS performance in a synchronous SRDF®
environment when the Enginuity™ 5772 single round-trip J0 performance enhancement feature is implemented.
January 2008
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Part Number H4164
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
EMC Enginuity 5772+
Applied Technology
2
Table of Contents
Executive summary ............................................................................................ 4
Introduction ......................................................................................................... 4
Audience ...................................................................................................................................... 4
Overview .............................................................................................................. 4
Testing methodology and description .............................................................. 5
Testing configuration ......................................................................................... 5
Testing results .................................................................................................... 6
IOPS with the COMMIT10 workload............................................................................................ 6
Response time components with the COMMIT10 workload........................................................ 6
IOPS with the COMMIT1 workload.............................................................................................. 7
Response time components with the COMMIT1 workload.......................................................... 8
Conclusion .......................................................................................................... 9
References .......................................................................................................... 9
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Executive summary
The latency inherent in EMC® SRDF®/Synchronous (SRDF/S) solutions can limit feasible replication
distances and make the implementation of such solutions challenging in performance-critical situations.
This latency is due to the propagation I/O delay introduced by source devices not receiving confirmation
that a write is complete until that write safely arrives at the remote site and a positive acknowledgement is
returned. This impact on write response time can be critical to DB2 on z/OS applications.
DB2 for z/OS online transaction processing (OLTP) applications typically have stringent service level
agreements that often require sub-second response times, and any delay in response time can impact
customer satisfaction. Managing I/O delays caused by latency is critical and marginal increases in I/O
response time to logging devices can negatively impact the entire DB2 system. Reducing latency reduces
I/O response time and can improve the performance of existing SRDF/S solutions for DB2 for z/OS. It can
also make an SRDF/S solution possible in situations where replication distance is a limiting factor.
This white paper describes SRDF/S testing of DB2 on z/OS with the new Enginuity™ 5772+ single roundtrip J0 performance enhancement enabled.
Introduction
SRDF/Synchronous (SRDF/S) is a high-performance, host-independent, real-time synchronous replication
from a (local) Symmetrix® array to one or more remote Symmetrix arrays, enabling the accurate mirroring
of data between the local Symmetrix array and its remote Symmetrix partners. Data is written to the global
memory of all arrays before the application I/O is acknowledged to the host as complete, ensuring the
highest possible data synchronization. Only when the write operation is complete at both locations are
further host writes accepted at the primary array.
This white paper evaluates the SRDF/S single round-trip J0 enhancement available in the Enginuity
5772.83.75 Service Release (SR). This enhancement to SRDF/S reduces I/O response time by addressing
the latency caused by transfer-ready frames in the Fibre Channel protocol. Previous Enginuity versions
required two round trips for every SRDF/S write, as the initiator (the source Symmetrix array) sends a
command frame and waits for the responder (the target Symmetrix array) to return a transfer-ready frame
before data transfer can begin. This resulted in an additional round trip between the source and the target,
causing the latency to be proportional to twice the round-trip time. SRDF/S devices can now run in
unsolicited mode, allowing the initiator to send a command frame immediately followed by the data. This
eliminates an entire round trip across the link for each write I/O. Significant benefit will be observed in
certain situations by eliminating this additional round trip, especially when link latency is high.
In typical OLTP environments, there are many transaction-commit events per second, and this paper
focuses on response to DB2 for z/OS log devices. For DB2 for z/OS, this results in a 4K record (control
interval) being externalized. The same control interval may be written several times. The SRDF/S single
round-trip enhancement dynamically evaluates each I/O and enables the feature based on latency and I/O
size. The 4K log record size that is written, which is within the parameters of the I/O size criteria (≤ 16K),
and the critical nature of log I/O response in a DB2 for z/OS environment, are the focus of this white paper,
which details the testing methodology, configuration, and RMF results.
Audience
This white paper is intended for DB2 on z/OS administrators and storage administrators managing
configurations with synchronous SRDF who wish to implement new features in Enginuity 5772
synchronous replication.
Overview
Any form of synchronous replication introduces a delay to writes received on the source array. The delay is
felt most with log writes on a DB2 on z/OS system as log writes usually occur synchronously with the
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
EMC Enginuity 5772+
Applied Technology
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application thread. The set of tests described in this paper are targeted at the improvement in writes to the
active log when the new SRDF/S single round-trip enhancement is enabled.
Testing methodology and description
All testing was conducted in an EMC lab environment with DB2 for z/OS. The results are expressed in the
form of percentage improvements seen with the feature disabled and then enabled for two different
simulated distances. The results from the lab environment may not be typical of those experienced in
specific customer configurations and environments.
Testing consisted of two threads running simultaneously, each thread randomly updating 50,000 rows in a 5
million row table. Two sets of jobs were executed:
•
The first set performed commit processing after 10 updates (identified as COMMIT10).
•
The second set performed commit processing after 1 update (identified as COMMIT1).
Each set was executed at two distance settings—50 kilometers and 100 kilometers—and DB2 was recycled
between each execution. The cache in the Symmetrix array was cleared between executions, the intent
being to mitigate any benefit of caching. RMF measurements were then analyzed.
As stated earlier, emphasis was placed on DB2 for z/OS log devices. DB2 for z/OS writes to devices
containing table information in a different manner and externalizes updates to tables based on buffer pool
size and buffer pool thresholds. When these updates are written, DB2 for z/OS arranges updates by page
sets and writes as many pages as possible. This can result in an I/O size that is greater than the I/O size
criteria used by the SRDF/S single round-trip enhancement.
If table update activity is random enough and buffer pool writes frequent, then I/O to tables can also benefit
from the SRDF/S single round-trip enhancement. These factors are very much site-dependent, and I/O to
tables is usually asynchronous and not as critical as I/O to log devices.
Testing configuration
The testing configuration consisted of two Symmetrix DMX™ 3-24 arrays running Enginuity 5772-82 and
is shown in Figure 1. The log devices were MOD9 R1 devices that were locally mirrored and connected to
a remote Symmetrix through an Empirix distance simulator. The remote devices were MOD9 R2 devices
that were locally mirrored.
Figure 1. Testing configuration
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
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Applied Technology
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Testing results
This section details the testing results measured using RMF.
IOPS with the COMMIT10 workload
Figure 2 depicts the number of I/Os per second (IOPS) for the workload that issued commits after 10
updates. Measurements are shown for both the 50- and 100-kilometer distances with the SRDF/S single
round-trip enhancement feature enabled and disabled. IOPS increased by 30 percent and 28 percent for the
50- and 100-kilometer distances, respectively, when the feature was enabled.
LOG IO (commit/10 updates)
30% more IO
IOPS
28% more IO
Feature Disabled
Feature Enabled
50 kilometes
100 kilometers
Figure 2. I/Os per second with the COMMIT10 workload
Response time components with the COMMIT10 workload
Figure 3 depicts response time components. The response time was reduced by 16 percent and 33 percent
for the 50- and 100-kilometer distances, respectively, when the feature was enabled. The reduction was due
to a decrease in the disconnect (DISC) time, which includes latency introduced by synchronous remote
copies. A reduction in DISC is expected when the SRDF/S single round-trip enhancement is enabled as
latency is reduced with this feature. This is also the primary reason for the increase in IOPS as shown in
Figure 2. A greater reduction for the 100-kilometer distance is also expected as there is more latency with
this distance.
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
EMC Enginuity 5772+
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Response Time
Log Response 50 KM(commit/10 updates)
CONN
DISC
PEND
IOSQ
16% reduction in
device response time
Feature Disabled
Feature Enabled
Response Time
Log Response 100km (commit/10 update)
CONN
DISC
PEND
IOSQ
33% reduction in
device response time
Feature Disabled
Feature Enabled
Figure 3. Log response time for 50 and 100 kilometers (with COMMIT10)
IOPS with the COMMIT1 workload
Figure 4 illustrates the same concepts as Figure 2, but with a greater logging rate. Commit processing was
invoked after each update as opposed to after every 10 updates as in the previous charts. Measurements are
shown for both the 50- and 100-kilometer distances with the SRDF/S single round-trip enhancement
feature enabled and disabled. IOPS increased by 18 percent and 15 percent for the 50- and 100-kilometer
distances, respectively, when the feature was enabled.
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
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Log IO (commit/1 update)
18% more IO
15% more IO
IOPS
Feature Disabled
Feature Enabled
50 kilometers
100 kilometers
Figure 4. I/Os per second with the COMMIT1 workload
Response time components with the COMMIT1 workload
Figure 5 depicts response time components. The response time was reduced by 28 percent and 33 percent
for the 50- and 100-kilometer distances, respectively, when the feature was enabled. Again, the reduction
was due to a decrease in disconnect (DISC) time.
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
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Response Time
Log Response 50 km (commit/1 update)
CONN
DISC
PEND
IOSQ
28% reduction in
device response time
Feature Disabled
Feature Enabled
Response Time
Log Respnse 100 kilometers (commit/1 update)
CONN
DISC
PEND
IOSQ
33% reduction in
device response time
Feature Disabled
Feature Enabled
Figure 5. Log response time for 50 and 100 kilometers (with COMMIT1)
Conclusion
The SRDF/S single round-trip enhancement can reduce latency in an SRDF/S Fibre Channel environment
based on distance and size of the I/O. This reduction improves response time for I/Os by decreasing
disconnect time.
The response time decrease for DB2 for z/OS logs may improve customer service levels in existing
SRDF/S Fibre Channel environments. In addition, it may be feasible to consider an SRDF/S solution for
greater distances that were previously prohibitive due to the inherent latency of the distance.
References
•
Application Benefit Data Sheet for DB2 for z/OS with 5772.83.75 Enginuity Service Release
•
New Features in EMC Enginuity 5772 for Symmetrix Environments white paper
DB2 on z/OS and Single Round-Trip J0 with Performance Enhancements in
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Applied Technology
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