Re: [courier-users] NFS server load thru the roof

On Sat, Oct 01, 2005 at 03:49:40PM -0700, email builder wrote:
> Hrm, not sure why list posts are taking so long, so I am, um,
> cross-posting... the original message was on this list anyway, and maybe if
> I'm lucky this will post within an hour...
>
> > We have much the same system setup and problems described here:
> >
> > http://thread.gmane.org/gmane.mail.i....general/21782
> >
> > Briefly, mail spool is mounted over NFS, everything runs smoothly until
> > we
> > turn IMAP on and server load goes off the scale (NFS client load 300, NFS
> > server load 10, with server in wait about 80% of the time). There are no
> > discernable errors in our logs, and everything still "works", albiet at a
> > snail's pace.
> >
> > Unfortunately, there are no responses to that thread. I am wondering if
> > anyone has any pointers about where is a better place to look/ask/rtfm.
> > From
> > all I have read, Courier itself should not have any locking or other issues
> > over NFS, and in fact, before we rolled out our full user base to NFS, we
> > tested with a few users, and IMAP was running just fine over NFS.
> >
> > Once we moved everything to NFS, however, with at least 10's of users
> > checking their mail regularly at most times, server load has gone to hell
> > in
> > much the same way detailed in that thread. I am guessing it is more of a
> > NFS
> > configuration thing, or possibly something with our file system on the NFS
> > server (reiserfs and RAID 5), but I'm a little wet-behind-the-ears on that
> > front, so even some baby hand-holding by someone who has the time and
> > patience would be highly appreciated. I mean, I don't even know if the
> > "sync" option for our mail spool NFS mount is best turned off....?
> >
> > Although it is curious that our MTA (postfix) does not incur any load hit
> > at all, and we are delivering hundreds of mails an hour at least. Should
> > Courier IMAP be that much more of a heavy hitter??

How big are your users's mailspools?

the MTA is only going to be delivering one message at a time, but
courier-imap is going want to check every file in the mailboxes the user
is accessing to get the message headers.

I had the same problem with Imap with the mail spool on AFS when the working
set size of the users reading mail via imap exceeded the local AFS disk
cache. It was solved by increasing the afs cache size. (I'm currently at
around a 10GB AFS cache).

What version of NFS are you using? I'm pretty sure that nfs is going to
require a network round-trip for *every* message in the currently active
imap folder, and it is likely not doing any local cacheing.


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