While troubleshooting another issue a week or two ago I came across this VMware knowledge base article. Having spent most of the time with other brand arrays in the past, I thought this was a pretty cool solution verses just increasing the queue length of the HBA. I would recommend setting this on your 3par BEFORE you get QFULL problems. Additionally, Netapp has an implementation of this as well.
Be sure to read the note at the bottom especially:
If hosts running operating systems other than ESX are connected to array ports that are being accessed by ESX hosts, while the latter are configured to use the adaptive algorithm, make sure those operating systems use an adaptive queue depth algorithm as well or isolate them on different ports on the storage array.
I do need to dig deeper how this affects performance as the queue begins to fill, not sure if one method is better than another. Is this the new direction that many Storage Vendors will follow?
Until then, the best advice is to do what your storage vendor recommends, especially if they say it is critical.
Here is a quick run through for you.
In the vSphere Client
Select the ESX host and go to the configuration tab and click on the Advanced Settings under Software.
In the Advanced Settings
Select the option for Disk and scroll down to the QFullSampleSize and QFullThreshold.
Change the values to the 3par recommended values:
QFullSampleSize = 32
QFullThreshold = 4