[plug] Mail Server thoughts

[Cameron Patrick]

Craig Ringer wrote:

> AFAIK, Linux NFS + Mail = Bad (splat!) . I certainly know that Cyrus
> IMAPd has dire warnings about using Linux's NFS implemementation
> anywhere near its mail spools.

If you use maildirs you should be fine using NFS, as there are no
locking issues to worry about.  Mbox is another matter entirely; it
provides lots of fun ways to lose your mail if the mailbox isn't
locked while a process is writing to it.  However, while NFS provides
some kind of locking mechanism, it doesn't work particularly well and
often either fails to lock things for no good reason, or claims to
have obtained a lock when it has done no such thing.  There are
actually two, not one, Linux NFS servers.  Both of them suck for
various reasons; however, the kernel-space one is the better of the
two as it supports NFS v3.  The user-space NFS server supports only
NFS v2 and AFAIK does not even attempt to do locking.

NFS also has some other fun not-quite-Posix semantics that can fool
applications which try to be too clever with the filesystem.  I'm not
aware of all the details but they seem less likely to be an issue with
mail spool.

I was at a talk today at LCA by Jeremy Allison of the Samba team
plugging CIFS / Samba as a good file sharing solution between Unix
machines, although it sounds like in some areas it's not quite there
yet and some of the locking details are a bit hairy.

Cameron.