Disks IOP's and VM

jfish

jfish

jfish

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24 May 2011
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After a lot of reading, I can work out the disk IOP's of a Windows 2003 server using performance counters - now if I plan to move this server to a virtual host on ESXi - how do I ensure the disk IOP's on the virtual server isnt compromised and thus I get poor performance, any recommended tools I can use in VM

all help much appreciated
 
knowlesy said:
Can you tell me how you figured that equation....
Click to expand...

? Not my post but it's a reasonable guess.

120 IOPS is a reasonable (if slightly low) estimate for a 15k SAS Drive, in a raid scheme which uses all spindles to read (in fact, basically in any scheme which doesn't need parity calculations to obfuscate things) you can just add it up like that.

We estimated similarly building an array of 160 drives in RAID10 and were within 10% of our predicted IOPS in testing (that is, the solution as built delivered 10% more than our design predicted)
 
bigredshark said:
? Not my post but it's a reasonable guess.

120 IOPS is a reasonable (if slightly low) estimate for a 15k SAS Drive, in a raid scheme which uses all spindles to read (in fact, basically in any scheme which doesn't need parity calculations to obfuscate things) you can just add it up like that.

We estimated similarly building an array of 160 drives in RAID10 and were within 10% of our predicted IOPS in testing (that is, the solution as built delivered 10% more than our design predicted)
Click to expand...

thanks for the update there :)
 
There is a small overhead with virtual disks, but it's not massive.
If you're really bothered you can use passthrough to let the VM talk directly to a storage controller, cutting out any overheads.

But considering if you're doing Virtualisation properly you'll be using a SAN (or at the least a higher end NAS) for storage IOPS shouldn't be of too much concern as you'll be looking at a minimum of 12 disks in RAID (probably RAID10).
And again you can passthrough to an iSCSI/FC HBA and talk pretty much directly to the LUNs themselves.

tl;dr = If you haven't had to troubleshoot issues caused by lack of IOPS yet then you don't need enough of them to be very worried about going virtual.

Yet another edit: I think you can actually see the IOPS generated by a particular VM in the ESXi/vCentre console anyway.
 
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