TECHNICAL REPORT: Performance Study This document has been archived and will no longer be maintained or updated. For more information go to the Storage Solutions Technical Documents page on Dell TechCenter or contact support.
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Preface EqualLogic PS Series arrays are easy to use and they optimize resources and simplify operations by automating many performance enhancement and network load balancing tasks. Additionally, PS Series arrays offer all-inclusive array management software, host software, and firmware updates at no additional license fees.
TABLE OF CONTENTS Revision Information........................................................................................................ iii Executive Summary............................................................................................................1 Introduction .........................................................................................................................1 What is EqualLogic Synchronous Replication (SyncRep)? .........................................
REVISION INFORMATION The following table describes the release history of this Technical Report. Report Date Document Revision 1.0 October 2012 Initial Release The following table shows the software and firmware used for the preparation of this Technical Report. Vendor Model Software Revision TM Dell EqualLogic PS6100X 6.0.0 TM Dell EqualLogic SAN Headquarters 2.2.11.6301 TM Force 10 S-Series S60 Switches OS Version: 1.0 Dell Dell Dell Application Software Version: 8.3.3.
EXECUTIVE SUMMARY Online Transaction Processing (OLTP) applications are by far some of the most mission critical applications in an enterprise. Protecting an organization’s OLTP application data and making it highly available during planned system maintenance like software or hardware upgrades as well as in unplanned disasters like network or power outage and building fire or flood is of paramount importance.
both the active and alternate volumes is hardened in the protected cache of the PS series members. If one pool is not available due to a power failure or other resource outage, volume data from the other pool can still be obtained. Listed below are some of the salient features/characteristics of SyncRep: SyncRep is the process of simultaneously copying all writes to a volume in a storage area network to a second volume so that an additional copy of data is available at all times.
SYNCREP TERMINOLOGY AND STATES SyncRep feature is enabled on a per-volume basis. For SyncRep-enabled volumes, the volume data exists simultaneously in two different pools. Snapshots will exist in whichever pool was the active pool at the time the snapshot was created. SyncActive – The pool to which iSCSI initiators connect when reading and writing volume data. SyncAlternate – When volume data is written to the SyncActive pool, the group simultaneously writes the same data to this pool.
TEST CONFIGURATION AND TOOLS In order to test a typical synchronous replication scenario in a campus environment a set of volumes containing a SQL Server 2008 database was configured with SyncRep from one EqualLogic storage pool (Pool 1) to another pool (Pool 2) within the same group (group A) that was separated by a simulated distance of one kilometer. We used Quest Benchmark Factory for Databases1 to simulate a TPC-C style workload on the test system using a SQL Server 2008 database.
Test goals: A. Simulate a TPC-C style database transactional workload while gathering application transactions per second (TPS) and end-to-end transaction response time data under increasing user load on a single PS Series array a. Without the SyncRep feature enabled b. With the SyncRep feature enabled B. Measure any performance impact of synchronous replication on the production database supporting the TPC-C transaction load for a specific number of concurrent virtual users a.
SQL SERVER Microsoft SQL Server 2008 SP1, 64-bit, provided the database services for the TPC-C clients. The SQL Server was hosted on a Dell PowerEdge R610 server with dual-socket hex-core Intel Xeon X5675, 3.07 GHz processors and 72 GB memory. As mentioned in the callout text box on Page 5, the SQL Server was configured to use a maximum of 4GB of cache. The SQL Server utilized the EqualLogic MPIO DSM for Windows from version 4.
Figure 2: EqualLogic test system configuration for a synchronously replicated campus site Note: This environment was setup just for the test lab purposes. Please refer to the Reference Architectures documents for a complete understanding of how to set up a highly-available configuration.
this group. Each database was assigned eight volumes. Of the eight volumes, six were data volumes, one was a log volume, and one was a tempdb volume. All eight volumes for a single database were part of a single PS series volume collection.2 Volume collection is useful when an operation needs to be performed simultaneously on multiple volumes. This feature helps maintain consistency in SQL Server environments because SQL database files are typically spread across multiple volumes.
The following three scenarios were tested using this configuration: A. For scenario A, a TPC-C style database transactional workload was generated while gathering transaction per second (TPS) and end-to-end transaction response time data under increasing user load on a single PS Series array. Four TPC-C benchmark clients simultaneously ran against each of these four databases. The workload was increased until the log latency exceeded 5 milliseconds.
which was in a different storage pool but within the same PS Series group. (Scenario A). Figure 3: Application TPS and Average transaction response time for a single member pool In Figure 3, the dotted lines represent results from test runs without SyncRep functionality enabled. The solids lines represent results from SyncRep test runs.
SyncRep test run doubled from that of the test run without SyncRep enabled. This is due to the fact that with SyncRep enabled, the writes that are written to the volume in SyncActive pool are simultaneously written to the volume in the SyncAlternate pool. Also, note that the write latency doubles from test 1 to test 2. However, there is negligible impact on the application TPS and the application average response time as seen in Figure 3 above.
independent copies of the same data. Since the write IOPs double, this will result in increasing the write latency on the storage system. The configuration parameters for these tests are shown in Table 3: Configuration Parameters EqualLogic SAN 6xPS6100X (2.5", 24 10K SAS drives,300 GB) 2xPS6100X (two EqualLogic storage Pools with one member in each Pool) Array configuration#1 A 1200 virtual user workload was run against a single member that was part of the SyncActive Pool.
Figure 6: Read IOPs stay constant while write IOPs double with SyncRep on single array as well on a three array configuration.
Once again, as mentioned in the text box on Page 5, the best way to interpret the results in Figures 6 and 7 is not to focus on the absolute TPS results achieved, but to focus on the percent difference between TPS results achieved with and without SyncRep. Key observations from these results can be summarized as follows: 1. IOPS scaled linearly with the addition of more arrays.
Switchover A pool switch for a SyncRep volume swaps the roles of the SyncActive and SyncAlternate pools. As part of the operation, the SyncActive pool becomes the SyncAlternate pool and the SyncAlternate pool becomes the SyncActive pool. When a pool switch takes place, iSCSI initiators are temporarily logged out of the volume. They can log back in again after the switch is complete. Depending on the initiator configuration, the initiators normally will automatically attempt to reconnect.
Figure 9: Switchover warning message The switch was performed with four Quest Benchmark Factory instances running a TPC-C OLTP workload against four SQL databases and completed almost instantaneously with no noticeable impact on the operations. There were no errors encountered during the switchover and the transactions that were taking place during the switchover completed successfully.
Pool2 (SyncActive) Pool1 (SyncAlternate) Figure 11: PS Series Group Manager GUI after switchover completes Table 4 summarizes the test results that were captured during the switchover tests: End-User Experience Attributes TPC-C Benchmark Performance Results Transaction Response Time Storage Read or Write I/O Latency Concurrent Users Log latency TPC-C TPS TPC-C IOPS SyncRep < 0.30 s 15 ms 4500 ≤ 5ms 236 5,226 SyncRep during Switchover < 0.
Average IOPS Reads: 1,242 Writes: 3,984 Average Latency Reads: 10.65 ms Writes: 8 ms Figure 12: SANHQ metrics for 3 PS6100X at 4500 user load with SyncRep enabled Average IOPS Reads: 1,118 Writes: 3,990 Average Latency Reads: 8.10 ms Writes: 6.25 ms Figure 13: SANHQ metrics for 3 PS6100X at 4500 user load with SyncRep enabled during switchover operation Failover Failover is a pool relationship change that is required because of a fault occurring in the SyncActive pool.
Figure 14: iSCSI Initiator and MSSQL Server Management Studio after failover CONCLUSION Many OLTP applications in real production environments also exhibit characteristics similar to the TPC-C benchmark workload tested in the simulated environment at Dell Labs. Protecting such SQL Server environments without compromising application performance is very desirable however, it can be difficult to achieve.
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