[Dovecot] Howto add another disk storage

[Stan Hoeppner]

On 7/4/2012 4:09 PM, Adrian Minta wrote:
> On 07/04/12 23:22, J E Lyon wrote:
>> On 4 Jul 2012, at 21:01, Adrian Minta wrote:
>>
>>> What is the best strategy to add another storage to an existing
>>> virtual mail system ?
>>> Move some domains to the new storage and create symlinks ?
>>> Switch to dovecot hashing ? But in this case what is the easy-east
>>> way to migrate ?
>>>
>>> Thanks for any suggestions or tips !
>> Are you using Volume Management (VLM) on the system, or do you have
>> regular partitions mounted? Is there any RAID or other factors to
>> consider . . in fact, a few details about your system might help :)
>>
>> ~ James.
> 
> No LVM and the RAID is done in the SAN appliance.

It absolutely kills me every time I see a mail server admin display
almost total lack of knowledge of his/her storage back end, or the
inability to describe it technically, in an email...

> My gut tells me that formatting a single huge 25TB partition is not the
> best way to go. 

What is this statement supposed to convey to us?  It makes no sense.

> That's why I consider having two different LUN's on two
> different SAN's mounted together as two directories. 

And this doesn't make sense either.

> A fsck and a
> recovery will work faster.

If you're having to run fsck on your filesystem on a regular basis,
you've have larger problems than storage provisioning.  What filesystem
are you using?

> The only issue is distributing maildirs. across the two file systems.

Here's the type of information and level of detail you need to provide
for any of us to intelligently assist you with this issue:

My SAN array is model X from company Y.  It has 12x 3TB drives
configured as a RAID6 array.  I have created a 5TB virtual drive and
exported it as LUN #X.  It houses the filesystem (extX/XFS/JFS) that
contains the mail store, which is now getting full.  I have 25TB of the
30TB net array space unallocated.  How can I best use this space to
increase storage space for Dovecot?

To which I would answer:

Unless your SAN array is an el cheap model, you should be able to simply
increase the size of the current virtual drive by adding a portion of
the 25TB of unallocated space.  Say you expand the virtual drive by
10TB.  The virtual drive is already exported as LUN #X, so the host to
which the LUN is unmasked simply now sees /dev/sdX as being 15TB total
size instead of 5TB.  At this point, simply grow the filesystem across
the additional 10TB of the "disk".  This negates the need for multiple
filesystems/namespaces and jumping through hoops to balance your maildir
workload across two separate filesystems.

This "on the fly" expansion capability is one of the biggest selling
points of SAN technology.  Surely your unit has such capability.

-- 
Stan