[bitfolk] Checking VPS performance

Hello,

Recently my VPS has begun performing certain IO intensive operations
notable slower, in some cases maildirs that can take less than a second
to open under ideal circumstances have been taking up to a minute to
load. I am told by Andy that iowait on the host server (barbar) is not
high at the moment, so it is likely to be something to do with the VPS
itself.

Can anyone suggest any diagnostic measures I can take to identify where
the performance issue is? I have never had to deal with such a
situation before, and Google is not offering a significant amount of
guidance.

Thanks,
Robert