zfs discuss - Jul 2011 - Adding mirrors to an existing zfs-pool]

Subject: Re: [zfs-discuss] Adding mirrors to an existing zfs-pool
Date: Tue, 26 Jul 2011 08:54:38 -0600
From: Cindy Swearingen <cindy.swearingen at oracle.com>
To: Bernd W. Hennig <consulting at hennig-consulting.com>
References: <342994905.11311662049567.JavaMail.Twebapp at sf-app1>

Hi Bernd,

If you are talking about attaching 4 new disks to a non redundant pool
with 4 disks, and then you want to detach the previous disks then yes,
this is possible and a good way to migrate to new disks.

The new disks must be the equivalent size or larger than the original
disks.

See the hypothetical example below.

If you mean something else, then please provide your zpool status
output.

Thanks,

Cindy


# zpool status tank
  pool: tank
  state: ONLINE
  scan: resilvered 1018K in 0h0m with 0 errors on Fri Jul 22 15:54:52 2011
config:

         NAME        STATE     READ WRITE CKSUM
         tank        ONLINE       0     0     0
             c4t1d0  ONLINE       0     0     0
             c4t2d0  ONLINE       0     0     0
             c4t3d0  ONLINE       0     0     0
             c4t4d0  ONLINE       0     0     0


# zpool attach tank c4t1d0 c6t1d0
# zpool attach tank c4t2d0 c6t2d0
# zpool attach tank c4t3d0 c6t3d0
# zpool attach tank c4t4d0 c6t4d0

The above syntax will create 4 mirrored pairs of disks.

Attach each new disk, wait for it to resilver, attach the next disk,
resilver, and so on. I would scrub the pool after resilvering is
complete, and check fmdump to ensure all new devices are operational.

When all the disks are replaced and the pool is operational, detach
the original disks.

# zpool detach tank c4t1d0
# zpool detach tank c4t2d0
# zpool detach tank c4t3d0
# zpool detach tank c4t4d0


On 07/26/11 00:33, Bernd W. Hennig wrote:
> G''Day,
> 
> - zfs pool with 4 disks (from Clariion A)
> - must migrate to Clariion B (so I created 4 disks with the same size,
>   avaiable for the zfs)
> 
> The zfs pool has no mirrors, my idea was to add the new 4 disks from
> the Clariion B to the 4 disks which are still in the pool - and later
> remove the original 4 disks.
> 
> I only found in all example how to create a new pool with mirrors
> but no example how to add to a pool without mirrors a mirror disk
> for each "disk" in the pool.
> 
> - is it possible to add disks to each disk in the pool (they have different
>   sizes, so I have exact add the correct disks form Clariion B to the 
>   original disk from Clariion B)
> - can I later "remove" the disks from the Clariion A, pool is
intact, user
>   can work with the pool 
> 
> 
> ??
> 
> Sorry for the beginner questions....
> 
> Tnx for help

On Tue, July 26, 2011 09:55, Cindy Swearingen wrote:
>
> Subject: Re: [zfs-discuss] Adding mirrors to an existing zfs-pool
> Date: Tue, 26 Jul 2011 08:54:38 -0600
> From: Cindy Swearingen <cindy.swearingen at oracle.com>
> To: Bernd W. Hennig <consulting at hennig-consulting.com>
> References: <342994905.11311662049567.JavaMail.Twebapp at sf-app1>
>
> Hi Bernd,
>
> If you are talking about attaching 4 new disks to a non redundant pool
> with 4 disks, and then you want to detach the previous disks then yes,
> this is possible and a good way to migrate to new disks.
>
> The new disks must be the equivalent size or larger than the original
> disks.
>
> See the hypothetical example below.
>
> If you mean something else, then please provide your zpool status
> output.
>
> Thanks,
>
> Cindy
>
>
> # zpool status tank
>   pool: tank
>   state: ONLINE
>   scan: resilvered 1018K in 0h0m with 0 errors on Fri Jul 22 15:54:52 2011
> config:
>
>          NAME        STATE     READ WRITE CKSUM
>          tank        ONLINE       0     0     0
>              c4t1d0  ONLINE       0     0     0
>              c4t2d0  ONLINE       0     0     0
>              c4t3d0  ONLINE       0     0     0
>              c4t4d0  ONLINE       0     0     0
>
>
> # zpool attach tank c4t1d0 c6t1d0
> # zpool attach tank c4t2d0 c6t2d0
> # zpool attach tank c4t3d0 c6t3d0
> # zpool attach tank c4t4d0 c6t4d0
>
> The above syntax will create 4 mirrored pairs of disks.
I was somewhat surprised when I first learned of this.  In my head, I now
remember it as "a single disk in ZFS seems to be treated as a one-disk
mirror".  Previously, in my head, single disks were very different objects
from mirrors!

I''m still impressed by the ability to attach and detach arbitrary
numbers
of disks to mirrors.  It makes upgrading mirrored disks very very safe,
since I can perform the entire procedure without ever reducing redundancy
below my starting point (using the classic attach new, resilver, detach
old sequence, repeated for however many disks were in the original
mirror).

-- 
David Dyer-Bennet, dd-b at dd-b.net; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info

On Thu, 28 Jul 2011, David Dyer-Bennet wrote:
> I''m still impressed by the ability to attach and detach arbitrary
numbers
> of disks to mirrors.  It makes upgrading mirrored disks very very safe,
Zfs mirrors are super-cool.  They are really flexible and recover 
quickly.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/