Re: Zpool surgery

Dan Nelson <dnelson_at_allantgroup.com> wrote:

> In the last episode (Jan 28), Fabian Keil said:
> > Ulrich Spörlein <uqs_at_FreeBSD.org> wrote:
> > > On Mon, 2013-01-28 at 07:11:40 +1100, Peter Jeremy wrote:
> > > > On 2013-Jan-27 14:31:56 -0000, Steven Hartland <killing_at_multiplay.co.uk> wrote:
> > > > >----- Original Message ----- 
> > > > >From: "Ulrich Spörlein" <uqs_at_FreeBSD.org>
> > > > >> I want to transplant my old zpool tank from a 1TB drive to a new
> > > > >> 2TB drive, but *not* use dd(1) or any other cloning mechanism, as
> > > > >> the pool was very full very often and is surely severely
> > > > >> fragmented.
> > > > >
> > > > >Cant you just drop the disk in the original machine, set it as a
> > > > >mirror then once the mirror process has completed break the mirror
> > > > >and remove the 1TB disk.
> > > > 
> > > > That will replicate any fragmentation as well.  "zfs send | zfs recv"
> > > > is the only (current) way to defragment a ZFS pool.
> > 
> > It's not obvious to me why "zpool replace" (or doing it manually)
> > would replicate the fragmentation.
> 
> "zpool replace" essentially adds your new disk as a mirror to the parent
> vdev, then deletes the original disk when the resilver is done.  Since
> mirrors are block-identical copies of each other, the new disk will contain
> an exact copy of the original disk, followed by 1TB of freespace.

Thanks for the explanation.

I was under the impression that zfs mirrors worked at a higher
level than traditional mirrors like gmirror but there seems to
be indeed less magic than I expected.

Fabian