User`s guide

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RAID 0+1. “Mirror of Stripes”. In this configuration, 2 RAID 0 arrays are mirrored with RAID 1, which
provides the fast read and write performance of RAID 0 and the fault tolerant features of RAID 1,
which addresses performance first and then fault tolerance.
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RAID 10. “Stripe of Mirrors”. In this configuration, multiple RAID 1 arrays are also striped, which
addresses fault tolerance first and then performance.
When you examine the RAID levels for use with SQL Server, follow these guidelines.
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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.
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SQL Server Data Files work best on RAID 0+1, but can be used on RAID 5 with little degradation in
performance.
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Multiple Disk channels are preferred. At the minimum, SQL Server Log files should be on a separate
physical channel from the SQL Server Data files, and if possible, neither should be mixed with OS or
Application files. For example, at a minimum SQL Server prefers 3 separate disk channels.
In addition to selecting the appropriate RAID configuration, consider disk interface and disk drive
performance. VCM data storage needs are usually low enough relative to commonly available drives that
the smallest drives are sufficient. Fast drives that have fast interfaces are important, along with having a
good number of “spindles” (drives) per RAID to distribute read, write, and seek activity across devices.
Most high-end drives are available in 10,000 RPM or 15,000 RPM spin rates. The faster spinning drives
usually seek faster and can achieve a higher sustained data throughput because more of the platter surface
area passes under the heads in each second.
Two primary interface technologies are suitable for use in high-throughput RAIDS.
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Ultra 320 SCSI, or U320 supports up to 320MB/s throughput per channel. The HP SmartArray 6404 can
support multiple U320 channels (four in the case of the SA6404) and on-board, battery-backed-up cache.
The cache provides for increased read and write performance because it allows the controller to batch
requests to the drives.
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Serial Attached SCSI (SAS) uses special 2.5” drives, and has a higher data rate than the U320, up to
600MB/s for newer controllers. SAS controllers typically have more ports than the channels in U320
controllers. Ports and channels are similar because they provide parallel data paths through the
controller. For example, an HP P600 provides 8 ports and each port is capable of 300MB/s.
For U320, the interface capacity is often the bottleneck. With SAS, the drives themselves can be the
bottleneck. SAS seems to provide better performance, flexibility, and scalability than U320 for VCM
installations. In addition to being faster and usually less expensive, SAS drives, although smaller, allow for
more spindles in the same rack space.
Regardless of the technology used, a consideration when designing RAIDs is that it is generally best to
utilize multiple channels or ports for high-throughput logical drives. For example, an 8-drive RAID 1+0 on
a single U320 channel provides 320MB/s of sustained throughput, while the same drives in a RAID with
four on each channel of a two-channel U320 controller (striped within the channels and mirrored between
channels) provides 640MB/s sustained throughput and offers additional fault tolerance to controller
channel or cable problems. If each quad of drives is in a different cabinet, this setup also provides fault
tolerance for cabinet failures.
An alternative to local storage for VCM is to use SAN storage. A common problem with SANs and VCM
previously was that many SANs are designed for file server or mailbox use and are not well-suited to
high-throughput OLTP-type activities. For a SAN to provide good performance with VCM, it must be
properly configured internally, and all devices between the SAN and the Collector must be adequate for
vCenter Configuration Manager Hardware and Software Requirements Guide
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