Zpool surgery

[Ulrich Spörlein]

On Tue, 2013-01-29 at 15:52:50 +0100, Fabian Keil wrote:
> 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

To wrap this up, while the zpool replace worked for the disk, I played
around with it some more, and using snapshots instead *did* work the
second time. I'm not sure what I did wrong the first time ...

So basically this:
# zfs send -R oldtank at 2013-01-22 | zfs recv -F -d newtank
(takes ages, then do a final snapshot before unmounting and send the
incremental)
# zfs send -R -i 2013-01-22 oldtank at 2013-01-29 | zfs recv -F -d newtank

Allows me to send snapshots up to 2013-01-29 to the "archive" pool from
either oldtank or newtank. Yay!

Cheers,
Uli