performance issues and problems: set Write back mode for your storage array for ideal performance

For performance you should have a battery backed cache for write back mode, which tells the OS that a write happened before it does because its saved on the cache
If you use write through mode, you will slow down the array because the os is then waiting for the disks to complete a write before continuing.



It might seem that this is obvious but if you are having problems check that out.
A user on the vmware forums was experiencing problems with their riad throughput and it was a mis config on the raid.

http://communities.vmware.com/message/2090651#2090651


A explanation from IBM on write back vs write cache for those interested:

Write back

For the write-back setting, the operating system sends data to the controller to write to a storage device. Subsequently, the controller sends a confirmation to the operating system before actually writing the data to the storage device. Doing so increases performance, but also contains an element of risk. For example, if there is a power failure, the data currently in the controller cache is lost. This is no risk when using a controller with a battery-backup cache. The battery preserves the data in the controller cache in the event of a power failure.

Write through

For the write-through setting, the operating system sends data to the controller to write to a storage device. Subsequently, the controller writes the data to the storage device; then, sends a confirmation to the operating system. This setting can decrease performance, but contains no risk of losing data.

http://publib.boulder.ibm.com/infocenter/eserver/v1r2/topic/diricinfo/fqy0_cwrcache.html