VMware VCENTER CONFIGURATION MANAGER 5.3 - SOFTWARE REQUIEREMENTS GUIDE Configuration page 77

1. SQL Server Log Files work best on RAID 10, and should never be used on RAID 5. If RAID 10 is not
available, RAID 1 should be used.
2. SQL Server Data Files work best on RAID 0+1, but CAN be used on RAID 5 with little degradation in
performance.
3. Multiple Disk channels are preferred. At the very minimum, SQL Server Log files should be on a
separate physical channel from the SQL Server Data files, and if at all possible, neither should be mixed
with OS or Application files (i.e., at a minimum SQL Server would like to see 3 separate disk channels).
Besides selecting the appropriate RAID configuration, disk interface and disk drive performance are also
considerations. Usually, VCM data storage needs are low enough, relative to commonly available drives,
that the smallest drives will be sufficient. The larger concerns are to have fast drives, with fast interfaces,
and to have a good number of "spindles" (drives) per RAID in order to distribute read/write/seek activity
across devices. Most high-end drives are available in 10,000 RPM or 15,000 RPM spin rates. The faster
spinning drives generally seek faster and can achieve higher sustained data throughput because more of
the platters' surface area passes under the heads in each second. Currently there are two main interface
technologies that are suitable for use in high throughput RAIDS:
Ultra 320 SCSI, or U320, is the older of the two. It supports up to 320 MB/s throughput per channel.
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Better controllers, such as the HP SmartArray 6404, support multiple U320 channels (four in the case of
the SA6404) and on-board, battery backed up, cache. The cache provides for much better read and
write performance, because it allows the controller to batch requests to the drives.
Serial Attached SCSI, or SAS, is the newer of the two and uses special 2.5" drives. The data rate for the
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SAS interface is higher than U320 (up to 600 MB/s for newer controllers), and SAS controllers typically
have more ports than U320 controllers have channels (ports and channels are similar in that they
provide parallel data paths through the controller). An HP P600, for example, provides 8 ports each
capable of 300 MB/s (assuming the drives could keep up).
In reality, for U320 the interface capacity is often the bottleneck, while with SAS it's generally the drives
themselves. Dollar for dollar SAS currently seems to provide better performance, flexibility, and scalability
than U320 for VCM installations. Besides being faster and generally less expensive, SAS drives, being
smaller, allow for more spindles in the same rack space.
Regardless of the technology used, one thing to consider when designing RAIDs is it is generally best to
utilize multiple channels/ports for high throughput logical drives. For example, an 8-drive RAID 1+0 on a
single U320 channel will only be able to provide 320 MB/s of sustained throughput, while the same drives
laid out in a RAID with four on each channel of a two-channel U320 controller (striped within the channels
and mirrored between channels) will give 640 MB/s sustained throughput and will also offer additional
fault tolerance to controller channel or cable problems. If each quad of drives is in a different cabinet, then
this setup also provides fault tolerance for cabinet failures.
An alternative to local storage for VCM is to use SAN storage. The common problem with SANs and
VCMin the past has been that a lot of SANs are designed for file server or mailbox use, and not well-suited
to high throughput OLTP-type activities. For a SAN to provide good performance with VCM requires
that it be properly configured internally, and that all devices between the SAN and the Collector be up to
the task as well. Note that a 4Gb HBA will be capable of slightly higher throughput than single Ultra 320
SCSI channel. On the other hand, for write activities, since mirroring and striping will be handled internally
at the SAN, the throughput of that 4Gb HBA is really more comparable to two and a half U320 channels.
Actually getting that throughput, though, depends also on the switches and links between the Collector
and the SAN, and, of course, on the drives and controllers in the SAN itself.
VMware, Inc.
Configuring SQL Server 2005 for VCM
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