[Dovecot] SSD drives are really fast running Dovecot

[Stan Hoeppner]

Timo Sirainen put forth on 1/16/2011 12:48 PM:
> On Sun, 2011-01-16 at 00:05 -0600, Stan Hoeppner wrote:
>> Using O_DIRECT with mbox files, the IOPS
>> performance can be even greater.  However, I don't know if this applies to
>> Dovecot because AFAIK MMAP doesn't work well with O_DIRECT...
>> ***Hay Timo, does/can Dovecot use Linux O_DIRECT for writing the mail files?
> 
> mmap doesn't matter, because mbox files aren't read with mmap. But I
> doubt it's a good idea to use O_DIRECT for mbox files, because even if
> it gives higher iops, you're using more iops because you keep re-reading
> the same data from disk since it's not cached to memory.
> 
> As for O_DIRECT writes.. I don't know if it's such a good idea either.
> If client is connected, it's often going to read the mail soon after it
> was written, so it's again a good idea that it stays in cache.
> 
> I once wrote a patch to free message contents from OS cache once the
> message was read entirely, because it probably wouldn't be read again.
> No one ever reported if it gave any better or worse performance.
> http://dovecot.org/patches/1.1/fadvise.diff

I'd gladly test it but I don't have the resources currently, and frankly, at
this time, the prerequisite knowledge of building from source.

-- 
Stan