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vCenter Configuration Manager Hardware and Software Requirements Guide
When considering SAN storage for VCM, not only should throughput (read and write speed) be
considered, but access latency should also be a concern. This is because VCM does a lot of relatively small
reads and writes. If the latency is too high, performance will be impacted as SQL Server waits for
responses to these small queries before it can move on to its next task.
Once a Collector has been installed, performance of the disk subsystem can be analyzed with Performance
Monitor. The main counters of interest will be the Physical Disk object's Disk Bytes/sec and Avg. Disk
Queue Length counters. Both of these counters can be monitored on a per-instance basis, to see what the
throughput is and how many threads are queued for each logical drive that is associated with VCM
activity.
The Disk Queue Length value is the best initial indicator about whether a logical drive has sufficient
throughput and access speed for the tasks of which it is being demanded. A good rule of thumb is that the
Disk Queue Length should not be above two times the number of processors in the system for more than
very short periods of time. There are other factors when viewing this counter, for instance, a logical drive
that is also used by the page file may show high queuing due to insufficient RAM in the system, but, for
the most part, this counter can be very useful in determining whether disk subsystem resources are
appropriate and also whether they are optimally arranged (disks per channel, RAID type, etc).
Using SQLIO to Determine IO Channel Throughput
In response to customer demand for more information on SQL Server IO requirements, Microsoft
developed a tool called SQLIO. It can be downloaded directly from Microsoft at the following URL:
http://www.microsoft.com/downloads/details.aspx?FamilyId=9A8B005B-84E4-4F24-8D65-
CB53442D9E19&displaying=en.
In order to accurately predict how well VCM will function on a given IO configuration, SQLIO should be
run prior to the installation of VCM to obtain a baseline of how well the IO subsystem functions.
Configure SQLIO with the following options to ensure an accurate report of IO throughput:
64K Block Size
n
4 Threads
n
2GB File Size minimum
n
Sequential IO
n
When executing SQLIO, ensure that you create baseline information for each IO channel (logical disk) that
will be used for VCM data as well testing both Read and Write operations.
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VMware, Inc.
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