IO Performance under VMware on LSI RAID controller

[Ivan Voras]

On 20/09/2013 15:08, Guy Helmer wrote:
> On Sep 19, 2013, at 11:25 AM, Guy Helmer <guy.helmer at gmail.com> wrote:
> 
>> Normally I build VMware ESXi servers with enterprise-class WD SATA drives and I/O performance in FreeBSD VMs on the servers is fine.
>> Whenever I build a VMware ESXi server with a RAID controller, IO performance is awful in FreeBSD VMs. I've previously seen this effect with VMware ESXi 3ware 9690SA-8I and 9650 RAID controllers, and now I'm seeing similar performance with a Dell 6/iR controller.
>>
>> Any suggestions would be appreciated.
>>
>> Guy
> 
> (Replying to self due to hint received off-list)
> 
> I seem to remember controllers mentioned previously by FreeBSD device driver developers that don't deal well with large I/O requests. It turns out that may be the case with VMware device drivers as well -- reducing the VMware Disk.DiskMaxIOSize value from its huge default of 32676KB to 32KB seems to have helped. Disk ops/sec in the FreeBSD VM are now peaking over 400/sec.

Interesting that the problem shows only on RAID controllers. Do you have
any ideas why this reduction helps (did you find a FAQ or a forum post)?
The default RAID stripe size in LSI is 64 KiB, maybe it would help even
further to align it also?

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