A common question from customers on LUN sizing for ESX hosts (written for EQL, however the MPIO limitations lie with ESX so this applies to other storage arrays also)
ESX performance issues may be resolved by simply following this guideline..
Q: In VMware ESX 3.x is it better to have one huge volume or multiple smaller ones?
Answer: Multiple smaller volumes are better. The ESX iSCSI initiator does not currently support MPIO. That is, the combining of GbE ports to connect to any one volume which would increase I/O to that volume. Therefore, any one volume will only have one GbE worth of connectivity. Multiple volumes will better use the available GbE interfaces.
There is also a VMware limit on the maximum number of outstanding IOs, with the ESX bundled iSCSI initiator that number is 32. Additional IOs will be paused until prior IO is completed. Multiple volumes mean more I/O can be going at the same time.
Lastly, certain operations, like starting/stopping VMs or doing VMotion, require that the ESX server have exclusive access to that VMFS volume for a short period of time. It uses SCSI reservations to accomplish this. Having one volume would mean that contention for reservations would be expected. This reduces ESX’s efficiency by delaying operations from different ESX servers.
When sizing your volumes, have no more than 15 – 30 VMs per VMFS volume. Less if the VM’s are going to be heavy consumers of I/O. For example ten Windows 2008 servers would typically require 40-60GB of disk space per VM. Leaving room for VMware snapshots means a volume size of 450GB to 700GB.
Reminder: ESX has a target (volume) limit of 64 targets per ESX server. This would include any snapshots or clones you bring online.
Hope this helps
Huzeifa Bhai
Hope this helps
Huzeifa Bhai
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