Configuring RAID for Optimal Performance

Configuring RAID for Optimal Performance Other Performance Factors

performance. Typically, sequential workloads benefit from using large strip sizes (512 KB or 1

MB).

With random types of access, the strip size depends on the typical access block size and on

data alignment. For example, if a database is using 16 KB records with 16 KB alignment, the

optimal strip size can be 16KB. For file- or web-server a large (512 KB or 1 MB) strip size can

be optimal. Software vendor documentation often provides recommendations on how to select

RAID strip sizes.

Note: Matching the strip size to the file system cluster size does not usually provide any benefit.

Data block or file sizes used by the application are usually more important. However, setting the

strip size smaller than the cluster size is not recommended.

5. Other Performance Factors

When measuring performance of a RAID subsystem, it is important to remove factors that can

limit the performance or cause variations in the performance.

5.1 Backup Battery Status

When doing write performance measurements in Write Back mode, it is important to check the

status of the battery and the Current Write Policy. When the battery is not fully charged or is in

the process of relearning, Write Policy will be automatically switched to Write Thru. This will

have big impact on write performance.

You can disable the Write Thru for a failed or missing battery option to make sure that the Write

Back mode is used regardless of the current battery status. In a production environment

disabling this option may cause data loss if power failure occurs when the battery does not have

sufficient level of charge.

5.2 Virtual Drive Initialization

For RAID 5/6/50/60 volumes it is important to perform Full Initialization of the volume before

doing performance measurements. On large virtual disks full initialization may take many hours

to complete. For performance measurements you can create smaller virtual disks.

For RAID 0/1/10 there is no need to perform Full Initialization before measuring performance.

However, it is important to disable Background Initialization (BGI) during measurements if Full

Initialization was not performed. Unless it is disabled, BGI will start automatically on RAID 1/10

volumes and will substantially reduce the RAID performance.

5.3 Patrol Read

Patrol Read helps to detect and reallocate bad blocks on hard drives and to prevent possible

data loss. Patrol Read generates substantial number of disk requests that may reduce the

RAID performance.

You should disable or enable Patrol Read depending on the purpose of your performance

measurements. You can also adjust the Patrol Read rate to reduce or to increase the priority of