On 08/06/15 20:28, Pierre Wieser wrote:

Hi all,

I currently have an almost full RAID 5 built with 4 x 2 TB disks.
I wonder if it would be possible to migrate it to a bigger RAID 5
with 3 x 6TB new disks.

Do you have a spare (I presume SATA) disk port?

I've imagined something like that :
- successively fail, remove a 2TB disk, add a 4TB disk, wait for end of recovery on three 2TB disks

If you've got a spare port, the newer mdadm's have, I believe, a "clone
and replace" option. Much better than failing then rebuilding.

If not, is it worth getting a SATA expansion board? If you've not got a
specialist mobo, surely a board is only going to cost a tenner or so,
and quality isn't *that* important seeing as it's only a temporary measure.

- at the end of this first phase, I have the same ~6TB RAID 5 clean group with 3 x 4TB + 1 x 2TB disks
- declare the last 2 TB disk faulty and remove it
- the RAID 5 group state goes to clean, degraded
- grow the RAID 5 group with --size=max option
- grow the RAID 5 group with --array-size=~12TB option
- last, grow the RAID 5 group with --raid-devices=3 and --backup-file=... options.

And I have tested it on a small test RAID 5 group.
As expected, this last command makes the RAID 5 group begins a reshaping operation.
But this one keeps stucked at zero.

So I have several questions :

Don't think I've answered any of them, but I might have raised new ones.
I just hope the tip saves you a bit of time.

Cheers,
Wol