How can I migrate RAID 1 to a new disk

[pokrakam]

I have a functioning but faulty drive in a RAID1 set that I would like to replace with a spare drive in another bay.
Instead of pulling out the drive and rebuilding, I'd like to minimise the risk of a fault during rebuild and expand the mirror set onto the new drive before decommissioning the faulty one. Seems obvious, but I can't seem to find any option to do this.

I tried setting the new drive as a spare, hoping for an option to say sync it and then drop the faulty one. No joy.
I tried expanding the volume set, but it automatically wants to change it to a RAID5 with no option to keep it mirrored.

Is there a way to do this?

[dolbyman]

No option like this

Pulling the faulty drive and rebuild is your only option

Have external backups at all time to prevent data loss

[pokrakam]

Thanks, that is unfortunate. It seems such an obvious option that should be technically feasible without too much effort.

For that matter the same should be possible with RAID5 or others too: If we have a RAIDn+spare and the systems says a drive is not healthy then we should be able to migrate to the spare safely and pull out the faulty drive when done.

[dolbyman]

RAID1 does not support spare, RAID5 and 6 do, so if you pull a faulty drive on a RAID with a spare, it will rebuild on the spare

[pokrakam]

Actually it does, I can set up a spare on my RAID1 set.
What I'm missing is the possibility to sync/rebuild without pulling the drive.

It's not a showstopper, the obvious route is to take a backup and replace. But that's time consuming and possibly risky if not using a backup. Plus there's the factor that something can change during the time between backup and rebuild complete. This is really relevant with 10TB+ drives with rebuild time in days...

[dolbyman]

let me rephrase that .. RAID1 for userfiles on QNAP does not support spares