When is necessary to increse or descreae the HBA adapter queue depth? What impact has this change to the system?
Increasing the queue depth of your HBA can be a trial and error sort of change. Increasing the queue depth might help with some VMs, and not others. It is best to tune this slowly monitoring any performance gains you might be getting. On the other side, if you increase the queue depth too much and you have a high IO VM, you could bog down your SAN and cause anything else connected to it to have unsatisfactory performance. If you have a dedicated SAN, this is not as big of an issue.
queue depth is one such parameter that you must modify only if you face some performance problems in queued commands.Monitor the vmkernel to see if it is queueing commands.when adjusting queue depths, be aware of limits on the maximum number of queues on the array, per fibre port or per lun.Exceeding the maximum might result in SCSI transport errors.
I agree with the last two posts , you don't really want to be changing the que deth on your HBA's due to the "knock on affects" it could have on your array.
How busy are you VMware LUN's on your SAN ?? This will also have an impact on your ESX hosts to , if your LUN's are running very "hot" i.e to many VM's on a data-store.
Use your SAN array tools , to check read /write ratio's
Hi, I agree with the previous posters, but there is a new feature in 3.5 U4 for queue lengths - take a look at Vmware KB1010922 but take note of the warning regarding other hosts/systems connecting that aren't using the same algorithm
Thank you very much for all replies!
I have found this http://communities.vmware.com/docs/DOC-6490
I do not have any performance issue yet. I was just curious