FreeBSD 9/ZFS: Striped Pool (2 disks) migrating to mirror (onto additional disk)

Christer Solskogen christer.solskogen at
Wed Jan 26 20:13:21 UTC 2011

On Wed, Jan 26, 2011 at 8:58 PM, Dan Nelson <dnelson at> wrote:
> In the last episode (Jan 26), Christer Solskogen said:
>> On Wed, Jan 26, 2011 at 9:42 AM, O. Hartmann wrote:
>> > My question is: is it possible to migrate the two-disk pool without data
>> > loss into a mirrored pool by adding the one 2TB-disk?
>> No, you cant create a two-way mirror of three disks with ZFS. The only way
>> of doing what you want by creating a gmirror (or by hardware raid) of the
>> two 1TB disks.
> You can, if you partition the 2tb disk into two smaller volumes, each the
> same size as one of the 1tb disks, then add one of those as a mirror of each
> original disk.  You'll end up with two mirrored vdevs in the pool.
> Performance probably won't be as good as a real mirror, though, since zfs
> doesn't know that two of its physical disks share a spindle.

Rememer that he also asked to do this without data loss. As far as I
know you cant remove devices from a vdev. If he is willing to accept
data loss there are a lots of ways of doing it.


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