What are the typical methods used to scale up/out email storage servers?
- by nareshov
Hi,
What I've tried:
I have two email storage architectures. Old and new.
Old:
courier-imapds on several (18+) 1TB-storage servers.
If one of them show signs of running out of disk space, we migrate a few email accounts to another server.
the servers don't have replicas. no backups either.
New:
dovecot2 on a single huge server with 16TB (SATA) storage and a few SSDs
we store fresh mails on the SSDs and run a doveadm purge to move mails older than a day to the SATA disks
there is an identical server which has a max-15min-old rsync backup from the primary server
higher-ups/management wanted to pack in as much storage as possible per server in order to minimise the cost of SSDs per server
the rsync'ing is done because GlusterFS wasn't replicating well under that high small/random-IO.
scaling out was expected to be done with provisioning another pair of such huge servers
on facing disk-crunch issues like in the old architecture, manual moving of email accounts would be done.
Concerns/doubts:
I'm not convinced with the synchronously-replicated filesystem idea works well for heavy random/small-IO. GlusterFS isn't working for us yet, I'm not sure if there's another filesystem out there for this use case. The idea was to keep identical pairs and use DNS round-robin for email delivery and IMAP/POP3 access. And if one the servers went down for whatever reasons (planned/unplanned), we'd move the IP to the other server in the pair.
In filesystems like Lustre, I get the advantage of a single namespace whereby I do not have to worry about manually migrating accounts around and updating MAILHOME paths and other metadata/data.
Questions:
What are the typical methods used to scale up/out with the traditional software (courier-imapd / dovecot)?
Do traditional software that store on a locally mounted filesystem pose a roadblock to scale out with minimal "problems"? Does one have to re-write (parts of) these to work with an object-storage of some sort - such as OpenStack object storage?
