Configuring RAID for Optimal Performance

Other Performance Factors Configuring RAID for Optimal Performance
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the requests. Patrol Read settings can be changed in Adapter Properties in RAID BIOS Console
or in RAID Web Console.
5.4 Consistency Check
Consistency Check is an important function that helps to detect inconsistencies in data stored
across hard drives in redundant RAID arrays and to identify possible sources of silent data
corruption.
Consistency Check generates substantial number of disk requests that may reduce the RAID
performance. You should disable or enable Consistency Check depending on the purpose of
your performance measurements. You can also adjust the Consistency Check rate to reduce or
increase the priority of the Consistency Check requests. Consistency Check settings can be
changed in Adapter Properties in RAID BIOS Console or in RAID Web Console.
5.5 Data Location on Physical Drives
When measuring sequential throughput, it is important to remember that the speed of the hard
drives depends on the location of the data.
The maximum sequential speed is achieved when reading or writing data in the beginning of the
hard-drive. When data is read or written to the end of the hard-drive, the sequential speed will
be 30%-40% lower.
If only a part of the hard drive capacity is occupied by the virtual disk or by the partition used for
the performance measurements, the random performance will be higher than if the whole hard
drive capacity was used. This happens because the hard drive heads make shorter movements.
It is important to remember about this factor affecting random performance when using several
partitions or several virtual disks in one array.
5.6 PCI Express* Slot
In configurations with many hard drives, the sequential throughput of the RAID may exceed the
bandwidth of the PCI Express* link. When using a RAID controller with a PCI Express x8
interface, make sure it is installed into a PCI Express* x8 (or higher) slot.
Typical bandwidth of a PCI Express Gen1 link is approximately 800 MB/s for a x4 interface, and
1600 MB/s for a x8 interface. In some systems it may be up to 10% lower depending on chipset
capabilities and BIOS settings.
5.7 Vibration
Vibration in the chassis can substantially impact hard drive performance. Vibration can be
caused by chassis fans or by other hard drives. Vibration is usually higher in rack-mount
systems, because smaller and higher speed fans are used. SATA drives are typically more
sensitive to vibration than SAS drives. Different models and even different sizes of the same
hard drive family can have substantially different sensitivity to vibration.