ZFS resize disk vdev

Andrew Snow andrew at modulus.org
Mon Dec 8 22:43:58 PST 2008

Bryan Alves wrote:
> I'm thinking about using a hardware raid array with ZFS, using a single disk
> vdev zpool.  I want the ability to add/remove disks to an array, and I'm
> still unsure of the stability of zfs as a whole.  I'm looking for an easy
> way to resize and manage disks that are greater than 2 terabytes.
> If I have a single block device, /dev/da0, on my system that is represented
> by a zfs disk vdev, and the size of this block device grows (because the
> underlying hardware raid expands), will zfs correctly expand?  And will it
> correctly expand in place?

In theory, this works fine - I have never tried it myself.  The only 
other way to expand a zpool is by adding more vdevs:  You cannot change 
a vdev once it is created other than to take it from a single disk to a 

Sun's ZFS best practice guide states that you should avoid a single disk 
vdev  because performance on the whole suffers and is worse than UFS.

I am going to publish some benchmark figures soon to back this up, based 
on testing I did with a 16 disk hardware RAID6.  ZFS was *alot* faster 
when I gave it the disks in a RAIDZ2 vdev.

- Andrew

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