ZFS: Parallel I/O to vdevs that appear to be separate physical disks but really are partitions

[Pawel Jakub Dawidek]

On Fri, Oct 22, 2010 at 03:52:36PM -0700, Eugene M. Kim wrote:
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> Greetings,
> 
> I run a FreeBSD guest in VMware ESXi with a 10GB zpool.  Lately the
> originally provisioned 10GB proved insufficient, and I would like to
> provision another 10GB virtual disk and add it to the zpool as a
> top-level vdev.
> 
> The original and new virtual disks are from the same physical pool (a
> RAID-5 array), but appears to be separate physical disks to the
> FreeBSD guest (da0 and da1).  I am afraid that the ZFS would schedule
> I/O to the two virtual disks in parallel thinking that the pool
> performance will improve, while the performance would actually suffer
> due to seeking back and forth between two regions of one physical pool.
> 
> 1. Will ZFS schedule parallel access to different top-level vdevs?

Yes, ZFS stripes requests over all top level vdevs.

> 2. If so, how can I suggest ZFS that certain vdevs should be treated
> not as separate physical disks but as partitions on the same physical
> disk?

Nope, that's not possible.

Instead of adding next 10GB disk maybe it is possible to grow the one
you have? ZFS should be able to grow automatically.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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