[horde] Bottleneck ? CPU or HDisk IO or RAM

[Zachariah Mully]

On Tue, 2009-02-03 at 01:04 -0800, Linux Advocate wrote:
> > 2) What IMAP server?
> 
> dovecot

Doesn't matter what you're going to throw at Dovecot, maildir eats I/O
like nothing else. You are definitely going to want to run plenty of
tests and get real familiar with your FS tuning options. Find at what
directory size it begins to fail. Then set something up to check for
mailboxes getting close to that number. Even the dir_index switch on
ext3 isn't going to help much.

I much prefer cyrus, but the tuning for that is even more complex. Even
so, I think it gracefully handles large loads by default.

> > 3) What configuration of SATA drives?  A single 1 TB drive will be
> > slower to read than a pair of 1 TB in a RAID0, which will be slower
> > than 4 half TB drives in a RAID10.  Good quality (ie expensive) SATA
> > RAID will be faster than cheap hardware RAID, and software RAID may be
> > faster than cheap hardware RAID.
> 
> 
> say 6 x 750 GB Sata disks

I see from another email you said RAID5. Don't do it. RAID10, possibly
multiple individual RAID10s to segment your users across. With maildir,
it's going to kill your I/O (every maildir message gets written at least
2 times before it's accessible to the user).

> > 4) What else is the host doing?
> 
> just dedicated for horde alone.

For Horde and IMAP? Separate the two. Horde doesn't really need all that
much horsepower to run, in comparison to your IMAP server. Spend the
money on that because people aren't going to care if webmail is down for
bit, but they will care if there email is complete down (assuming that
webmail isn't the only access point).

And figure out your backup strategy before you deploy. Backing up and
restoring a mail server with X million individual files has it's own
unique issues.

Z