[Dovecot] Howto add another disk storage

[Stan Hoeppner]

On 7/5/2012 2:44 AM, Adrian M wrote:

> Hi Stan,
> I know how to add drives to the storage and how to grow the existing
> filesystem, but such big filesystems are somehow new to mainstream
> linux. Yes, I know some university out there already have pentabytes
> filesystems, but right now stable linux systems have trouble
> formatting ext4 partition over 16T.
> All this is telling me that is safer to have two or tree smaller
> filesystems than a big one. Dovecot has a nice feature for this
> "Directory hashing" http://wiki.dovecot.org/MailLocation/

At 16TB+ scale with maildir you should be using XFS on kernel 3.x, not
EXT4.  Your performance will be significantly better, as in 30% or much
more.  The typical XFS filesystem in the wild today is 50TB+ and there
are hundreds of XFS filesystems well over 100TB deployed around the world.

NASA has XFS filesystems of 380TB and 535TB, and also has multiple 1PB+
CXFS (cluster XFS) filesystems.  20TB is a tiny snack for XFS, 500TB is
lunch, 1PB is a big supper.  A single XFS can scale to 16 Exabytes, or 1
million terabytes, though the largest deployed so far that I'm aware of
is NASA's 535TB XFS.  It'll scale to anything you'll ever throw at it,
and much more.

> What I don't know is a nice way to migrate from a single directory no
> hashing to more than one and hashing.

It's a good time to migrate to XFS.

-- 
Stan