Cyrus mail spool entirely on SSD

[Rob N ★]

On Thu, 20 Oct 2016, at 05:28 AM, Michael Ulitskiy via Info-cyrus wrote:
> My question is: assuming cost is not an issue, would it be advisable
> to put an entire cyrus mail spool on SSD?
> I'm thinking about combinining multiple SSDs into RAID10 to further
> increase performance.

At FastMail we have our mail spools on SSDs, in RAID10. We use Intel DC
S3700 which, while on the expensive side, have been incredibly reliable
and fast. They're all still 6G SATA; we're still looking at NVMe (with
some enthusiasm).

We actually have too much mail right now to use SSDs for the entire
spool, so we use Cyrus' tiered storage facility to keep the most recent
(last week) mail on the SSD, and the rest on spindles (WD Gold 4TBs).
There's a cyr_expire job that runs periodically to move old stuff down
to the spindles. Metadata and caches are exclusively on the SSDs.

The search indexes are spread across disks; the fastest in ramdisks, the
SSDs, then spindles again. Again, there's a regular job to eject older
stuff down the stack. Ramdisks are used to make search response on
recent messages ridiculously quick. There is an operational cost in that
in order to cleanly shutdown the machine, you have to compact down the
ramdisk search indexes and if you don't, you have to reindex the entire
spool. It's pretty rare for that to happen though, and since the search
index is not a primary data source, its an acceptable risk.

So yes, SSDs are a great idea. I'd have _everything_ on SSDs if it were
cost-effective :)

Cheers,
Rob N.
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