On Wed, Feb 17, 2016 at 12:49 AM, Alessio Cecchi alessio@skye.it wrote:

Hi, I'm are running a classic Dovecot setup:

About ten thousand connected users mailbox in Maildir format shared via NFS (NetApp) Director for POP/IMAP Delivery via Dovecot LDA

All works fine but sometimes I see a spike on the load of POP/IMAP servers and high disk usage (close to 100%) on NFS NetApp.

When this happens on NFS stats (of POP/IMAP) I can see an high volume of "lookup, remove, rename" requests.

Example (avg is during normal load, max is request number during the spike):

Lookup avg 100 max 700 Remove avg 50 max 300 Rename avg 50 max 300 Getattr avg 200 max 250 Total NFS avg 600 max 1800

I think that some users are doing some kinds of "intensive" operations on their mailbox but what and who?

I am currently using "iotop" to monitor the activity of individual users but I can't figure out who is causing the high number of I/O requests.

One suggestions is that I'd walk those directories and see if someone has a mailbox with 100k files in it.