User`s guide

the task. A 4Gb HBA is capable of slightly higher throughput than the single Ultra 320 SCSI channel. For
write activities, since mirroring and striping is handled internally at the SAN, the throughput of the 4Gb
HBA is more comparable to two and a half U320 channels. Getting that throughput depends also on the
switches and links between the Collector and the SAN and between the drives and the controllers in the
SAN.
When considering SAN storage for VCM, throughput (read and write speed) and access latency should be
considered. Both are important because VCM performs many 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 perform the next task.
After you have installed a Collector, analyze performance of the disk subsystem using Performance
Monitor. The main counters of interest are the Physical Disk object’s Disk Bytes/sec and Average Disk
Queue Length counters. You can monitor both of these counters on a per-instance basis to determine the
throughput and the number of threads that 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 being required. Typically, the Disk Queue Length should not be
more than twice the number of processors in the system for more than very short periods of time. When
viewing this counter, a logical drive that is also used by the page file may show high queuing due to
insufficient RAM in the system, but this counter can be very useful in determining whether disk subsystem
resources are appropriate and whether the resources are optimally arranged, such as disks per channel,
RAID type, etc.
Use SQLIO to Determine IO Channel Throughput
SQLIO is a tool that determines the I/O capacity of a SQL configuration. To predict how well VCM will
function on a particular IO configuration and to obtain a baseline of how well the IO subsystem functions,
run SQLIO before you install VCM.
After you install SQLIO, configure these SQLIO settings to ensure an accurate report of IO throughput:
n
64K Block Size
n
4 Threads
n
2GB File Size minimum
n
Sequential IO
When you execute SQLIO, ensure that you create baseline information for each IO channel (logical disk)
that will be used for VCM data as well as testing both Read and Write operations.
Procedure
Download SQLIO from the Microsoft download site.
Configure SQL Server for VCM
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