5.8

n RAID 0+1. Mirror of Stripes. In this configuration, two 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.
n RAID 10. Stripe of Mirrors. In this configuration, multiple RAID 1 arrays are also striped, which
addresses fault tolerance first and then performance.
Using the RAID Levels with SQLServer
When you examine the RAID levels for use with SQL Server, follow these guidelines.
n SQL Server log files work best on RAID 10 and should never be used on RAID 5. If RAID 10 is not
available, use RAID 1.
n SQL Server data files work best on RAID 0+1, but can be used on RAID 5 with little degradation in
performance.
n 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. Where possible, do not mix the log files or data files
with the OS or application files. For example, at a minimum SQL Server prefers three separate disk
channels.
Disk Interface and Disk Drive Performance
In addition to selecting the appropriate RAID configuration, consider the 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 an
adequate 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.
n Ultra 320 SCSI, or U320 supports up to 320MB/s throughput per channel. The HP SmartArray 6404 can
support multiple U320 channels (four for the SA6404) and on-board, battery-backed-up cache. The
cache provides increased read and write performance, because it allows the controller to batch requests
to the drives.
n Serial Attached SCSI (SAS) uses special 2.5” drives and has a data rate up to 600MB/s for newer
controllers, which is higher than the U320. 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.
When you design RAIDs, regardless of the technology, a consideration is to use 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 that has four drives on each channel of
a two-channel U320 controller that is 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 provides fault tolerance for cabinet
failures.
An alternative to local storage for VCM is to use SAN storage. A common problem with SANs and older
versions of VCM 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 VCM Collector must be adequate
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