Cyrus, clusters, GFS - HA yet again

[Simon Matter]

> Hello,
>
> maybe I have understood GFS wrong, but isn't it ment to stripe data of
> several servers instead of mirroring them but make it accessable from
> several servers? If one server goes down, then you can only access the
> metadata from the GFS metadata server, but not the file itself from the
> server.
>
> Even with a cyrus murder cluster you cannot have shared mailboxes with
> different domain names (<department>.university.xx). With Cyrus each
> mailbox belongs to a certain backend-server. To be completly independed
> you need a big SAN (or maybe GFS) with Maildirs and then you can add an
> arbitrary amount of servers for deliveries, spamfilters, virus scan,
> imap and pop3 and make snapshots and backups of the complete storage.
>
> However, that way you will get into trouble with the calculation of
> quota at each delivery of a new messages, because it takes very long to
> sum all sizes of the messages within a mailbox as it cannot to be done
> locally on the harddisk but has to be done over the network (through the
> GFS or SAN) and if a maildir contains several hundrets or thousand

Now I think you really mix things up. 1) AFAIK quota is a per user
database which is updated whenever there is a change to the users mailbox.
Cyrus only scans all mail for their size with you do a "quota -f" after
something messed with your mailspool. 2) You have to consider GFS volumes
a local storage because it is usually on SAN which is also virtually local
storage. It really has nothing to do with networked filesystems like NFS.
AFAIK the trick with a GFS clustered Cyrus system is that you have two or
more independant Cyrus servers sharing the same metadata and message store
on the block device level, and not caring about each other, which means
they all serve tha same mailboxes/users. IIRC there are people running
Cyrus servers that way on other systems like Tru64 or Veritas cluster.
I think you have mixed up block device level shared filesystems with NFS
shared systems, which for example can be used for maildir based systems.

Regards,
Simon