How to understand NFS lookup (requests) spike?

[Mark Moseley]

On Wed, Feb 17, 2016 at 12:49 AM, Alessio Cecchi <alessio at 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.