I recently had this exchange with EqualLogic tech support about the IO Operations Limit:

"In regards to setting the iops to 3, In asking around on this , we do not have any documentation that specifically instructs to change this value to 3 . We do have a similar setting in RedHat that we have recommended changing to 300 . My lead has been in discussion with other L3 techs , the unofficial consensus is that 3 may be to low of a setting."

If someone from Dell/EqualLogic could clarify what the correct setting should be, please post it here!

Thanks,

-Rob

Hey Rob,

I forwarded your post to one of EqualLogic experts, and this was his comment:
Basically, the default settings for VMware MPIO are set so high that MPIO in many cases does not help performance very much. Customers who want to have MPIO activated sooner should lower the value – the number 3 is simply a suggestion, not a rule, and in some cases a number such as 300 may be appropriate. In others a lower number such as 10, 50 or 100 might work best. The tradeoff comes in the form of overhead in vSphere for path switching vs. the potential advantage of having lower queue depths on the IO paths. The customer is encouraged to try various values to determine what the optimal setting for their environment is since no two environments are exactly the same. SANHQ can be used to monitor latency and network retransmits to determine if changing the value has any effect for them.

Jeff

Thanks Jeff. I feel it might be best to change the number to something higher than 3, probably 300 would be a better place to start, which is still much lower than the default. I'm looking forward to SANHQ 2.0 which should make it even easier to tell if the change made an improvement or not.