[Dovecot] SSD drives are really fast running Dovecot

[Eric Rostetter]

Quoting David Jonas <djonas at vitalwerks.com>:

> I've been considering getting a pair of SSDs in raid1 for just the
> dovecot indexes.

While raid-1 is better than the raid-0 of the previous poster, do you
really want to slow down your fast SDDs with software raid-1 on top of them?

> The hope would be to minimize the impact of pop3 users
> hammering the server.

> Proposed design is something like 2 drives (ssd or
> platter) for OS and logs

The OS is mostly cached, so any old drive should work.  Logs are lots
of writes, so a dedicated drive might be nice (no raid).  Be sure to
tune the OS for the logs...

> 2 ssds for indexes (soft raid1),

I'd probably just go with one drive, maybe have a spare as a cold- or  
hot-spare
in case of failure.

> 12 sata or
> sas drives in RAID5 or 6 (hw raid, probably 3ware) for maildirs. The

I'd say either raid-6 or raid-10 for this, depending on budget and size
needs.

> indexes and mailboxes would be mirrored with drbd. Seems like the best
> of both worlds -- fast and lots of storage.

drbd to where at what level?  There was a some other discussion about this
which basically said "Don't use drbd to mirror between VM guests"
which I agree with.  If you want to do this, use DRBD between VM servers
(physical hosts) and not between VM guests (virtual hosts).

I do use a VM cluster with DRBD between the physical hosts, but not for
mail services, and it works fine.  Doing DRBD inside the virtual hosts
though would not be good...

> Does anyone run a configuration like this? How does it work for you?

No.  I do 2 nodes, with DRBD between them, using GFS on them for both
the mbox files and indexes...  No virtualization at all...  No SSD drives
at all...

> Anyone have any improvements on the design? Suggestions?

Only my advice about where to drbd if you are virtualizing, and what
raid levels to use... But these are just my opinions and your milage
may vary...

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Go Longhorns!