Gluster users - Apr 2016 - Performance tuning: How do I measure the performance of IMAP-on-Gluster?

Hi everyone.

My Gluster cluster is finally behaving fairly well, CPU, disk and 
network performance has returned to a stable state, and I'd like to 
start doing some performance tuning. To do that though, we need to have 
some metrics to see if the changes we make, are making any difference at 
all.

The basic problem I'm trying to solve is how slow IMAP and Webmail are 
on our high-availability cluster. All of our e-mail is stored in Maildir 
format on the Gluster drive, and as a result, using Webmail to "read the 
next message" is something that takes a couple of seconds, even if we go 
back to a file that's been read recently and should be cached. I'm not 
entirely sure how to measure that with the `time` command on the Unix 
command line in any consistent manner, and other commands (like `ls` or 
`cat` or `du`) do work a lot faster if repeated within a short period of 
time. It appears to be the case that producing consistent results 
(especially the results that matter the most to the customers) basically 
requires an IMAP connection to read a message.

I need some other ideas about how I can perform this test. Your help 
will be much appreciated.