Scaling of imap servers

Eric Luyten Eric.Luyten at
Fri Jun 17 04:03:33 EDT 2011

On Thu, June 16, 2011 6:18 pm, Vincent Fox wrote:
> On 6/16/2011 7:24 AM, Pascal Gienger wrote:
>> 20K users with 20G each = 400 TB. With zfs compression perhaps 300 TB.
> I dunno, I find that people use FAR FAR less than their quota on average.
> Sure you've got the 1 doctor who sends a bunch of X-rays or something
> but most people wouldn't fill up a 1-gig quota unless they were trying to. I'd
> be curious to know what the statistics are for actual USAGE by email users on
> a really big install.
> We could give our users unlimited IMO and it wouldn't make a difference
> worth losing sleep over.  I view quota as more of a tool to make slobs throw
> out some junk occasionally, and if they really need more they will phone in
> and we'll raise their quota.  Something like 20K users here and using only
> about 35% of our 3TB of storage.  Using ZFS compression so that gains us
> efficiency.  OK there's the single instance store savings too but I don't know
> how to quantify that effect.  We also keep 14 days of snapshots in the pools
> for easy recovery of "lost" emails.


68,000 users here, 4.5 TB mail uncompressed (with ZFS compression 2.7 TB)
This averages to roughly (only) 66 Megabytes per user.

For non-student IMAP client users (we also support POP3 but those people
are kindly requested to reduce their keep-messages-on-server timeframe)
we up the mail quota to 2.5 GB on simple request (and even proactively).

We currently have only two users at 2.5 GB quota, five at 1.5 TB and about
fifty at 1.0 GB, making for a very small minority indeed.

We keep 120 days of snapshots in the spool and this consumes 60% extra space.

Eric Luyten, Computing Centre VUB/ULB, Brussels.

More information about the Info-cyrus mailing list