[Dovecot] Howto add another disk storage

Kaya Saman kayasaman at gmail.com
Thu Jul 5 12:45:00 EEST 2012

On Thu, Jul 5, 2012 at 10:35 AM, Stan Hoeppner <stan at hardwarefreak.com> wrote:
> 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

Other good operating systems for large filesystems are FreeBSD with
either UFS2 or ZFS, or Solaris with ZFS.

But then one must think, do I really want to switch OS?

As a personal preference I would go FreeBSD route as dovecot is easily
available through 'Ports'. Even with miniscule stroage (20GB) for my
new Dovecot IMAP server here at work FreeBSD 8.2 x64 running on VMware
using ZFS for the 'extra' 20GB disk is performing pretty well.

Both UFS2 and ZFS can be snapshotted although ZFS has some
functionality which is really cool but one will need to know how to
set it up properly. Hence Zeta Byte Filesystem :-)

UFS2 tends to perform faster.... however.



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