LARGE single-system Cyrus installs?
brong at fastmail.fm
Thu Nov 15 18:39:12 EST 2007
On Thu, Nov 15, 2007 at 01:29:54PM -0500, Wesley Craig wrote:
> On 14 Nov 2007, at 23:15, Vincent Fox wrote:
> > We have all Cyrus lumped in one ZFS pool, with separate filesystems
> > for
> > imap, mail, sieve, etc. However, I do have an unused disk in each
> > array
> > such that I could setup a simple ZFS mirror pair for /var/cyrus/
> > imap so
> > that the databases are in their own pools. Or even I suppose a UFS
> > filesystem with directio and all that jazz set.
> About 30% of all I/O is to mailboxes.db, most of which is read. I
> haven't personally deployed a split-meta configuration, but I
> understand the meta files are similarly heavy I/O concentrators.
Which is a good argument for checkpointing it (gah, hate that term -
it's so non-specific. I've spent some time working on terminology
maps for this stuff, and "repack" is the current winner, mainly due
to be shorter than the runner up "consolidate")
What was I saying again? Oh - yes. Current skiplist metric is that
the mailboxes.db has to be be twice the size of the last checkpointed
size plus 16k before it re-checkpoints. Given that a checkpoint takes
approximately 2 seconds on our systems, and it means that you're not
seeking all over the place any more, it would almost certainly be a
That said, we don't have a single machine where the memory pressure
is tight enough to ever push mailboxes.db out of the cache, so it's
not ever going to be hitting the disk for reads anyway!
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