Cyrus, clusters, GFS - HA yet again

[Marten Lehmann]

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 
messages it takes really long and will slow down the whole system 
because of i/o waits. Look for an smtp-server and imap/pop3 server that 
can handle maildirsizefile (Maildir++), then this problem would be 
solved. But as far as I know there are no imap/pop3 servers available 
that have the same feature set as Cyrus (indices, quota system, shared 
folders, etc.) so you have to make a choice.

Regards
Marten