On 11 Jun 2008, at 22:18, Jeroen van Aart wrote:
> But why not use a raid1 instead of the one disk? It will increase
> redundancy even more. Now I understand that in your load balanced
> setup
> if one or a few servers' disks would die the system would still
> function. But you would have to clone/recreate the system and bring it
> back up. With a raid1 you would only have to replace the broken disk
> and
> that's it (or if you had a hot spare you had to do nothing).
I have to say I am getting less convinced by RAID 1 on systems. Its a
really good idea in theory, but in practice disks appear to be able to
come up with failure modes outside of what the controller or software
expects, and of course these failure modes are less well tested.... Add
to that the controllers for hardware RAID sometimes appear to find their
own failure modes. Designing so that the complete unit (ie one box with
internal disk etc) is disposable and is just removed from service when
there is a problem certainly has its attractions.
>> total. Maildirs for the users are stored on NetApp filers.
>
> Netapp uses NFS I assume? How well does it work with imap? As far as I
> know using imap on anything but unix format mailboxes on a networked
> filesystem like NFS can cause problems due to file locking and such.
Maildir is locking free. (Well thats strictly untrue - it uses directory
level concurrency control within the kernel but thats invisible to you).
Imap on NFS (particularly NetApp NFS) using Maildir is hardly new stuff
- thats how the Planet/Freeserve mail system was implemented 10 years
ago - that scaled to something over 3 million users then. You can add
some tweaks to Maildir to reduce the NFS load (see Yann Golanski's paper
on the subject from around the turn of the millennium). NFSv3 may have
made some of these tweaks less useful.
Nigel.
--
[ Nigel Metheringham Nigel.Metheringham@??? ]
[ - Comments in this message are my own and not ITO opinion/policy - ]
