Well I disagree, I found a post (not sure where), but I remember reading that read ahead only applies to small random files. Since ESX uses LARGE VMDK files, a read ahead won't work, and it can actually kill performance somewhat.
One thing I need to mention is that this assumes your VM's are running locally to the machine. If you have a SAN, NONE of this will have ANY affect. The SAN has it's own cache controller, not affected by the PE internal card.
Turn read ahead off, and set cache to write through, not write back. That's how I have ALL my PE 2950/R900 machine's. Also turn off the CPU features for caching also. Using write back is more secure.
Write-Back. When using write-back caching, the controller sends a write-request completion signal as soon as the data is in the controller cache but has not yet been written to disk. Write-back caching may provide improved performance since subsequent read requests can more quickly retrieve data from the controller cache than they could from the disk. Write-back caching also entails a data security risk, however, since a system failure could prevent the data from being written to disk even though the controller has sent a write-request completion signal. In this case, data may be lost. Other applications may also experience problems when taking actions that assume the data is available on the disk.
Write-Through. When using write-through caching, the controller sends a write-request completion signal only after the data is written to the disk. Write-through caching provides better data security than write-back caching, since the system assumes the data is available only after it has been safely written to the disk.
