Maildir on ZFS

[Mason Loring Bliss]

On Fri, Aug 28, 2020 at 06:45:00PM -0400, mike tancsa wrote:

> But I tried on a very busy sftp server where some directories had
> 500,000+ files in them.  It didnt seem to make a difference performance
> wise for me, at least when fiddling with min cache sizes etc.

That's encouraging. I guess that's the anwer - try it and see if there are
any observable issues. I've seen lots of complaints about IMAP on IRC and
vague noises when searching online, but nothing definitive. Maybe there is
nothing definitive.


On Sat, Aug 29, 2020 at 10:29:24AM +0200, Ronald Klop wrote:

> It depends on the clients also. Do they retrieve mail once, store it
> locally and only check the server for updates, than metadata might be
> enough, but if it is mostly webmail clients which retrieves the same mail
> multiple times, than caching data is probably beneficial.

It's mostly Mutt and Thunderbird. I'm not wholly familiar with what
Thunderbird does, but Mutt just caches headers and looks for changes.


> But it also depends on the amount of data you store on what medium
> (HDD/SSD/RAID) and how much memory your server has.

Hm? RAID? This'll be ZFS mirrors for this application. Everything I run is
either a mirror or raidz2 lately. Lots of memory. Spinning rust. Just ZFS
and imapd running in a jail, where the jail has one dataset to itself and
doesn't important anything over the network.


> NB: Maildir is very (Z)FS friendly by having a lot of static data on disk.
> Dovecot creates some indices for fast retrieval of metadata.

It'll almost certainly be Dovecot, and that sounds encouraging. (I used to
run Courier stuff and that's often tempting, but Dovecot has been pain-free
for years now.)


> The other advice is: test your own system. In the other reply I saw advice
> about how to look at cache statistics. ZFS is very fast without tuning
> already.

Yar. I was mostly wondering if there were any obvious pitfalls or things
that I'm very likely to hit, but it looks like there probably aren't.

Once I've got things migrated and seen it in action I'll gather some data
and share my results.


Thank you both for your input.

-- 
Mason Loring Bliss    mason at blisses.org
They also surf, who only stand on waves.
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