Re: MDRaid Rollback

[Wols Lists <antlists@youngman.org.uk>]

On 24/03/21 14:44, Andy Smith wrote:
> But, this being a RAID-1 you have at least two devices so wouldn't
> it be safer to:
> 
> - Fail out one device
> - Zero that device
> - Create new filesystem on the removed device
> - Copy data onto it from the still-running array that is currently
>   degraded
> - Use new filesystem for whatever you wanted

Better yet just get another drive and copy it across. You can always do
a "dd if=/dev/md0 of=/dev/sdc1" or whatever is appropriate. (And before
anyone asks, I'm planning to copy a filesystem that way, because it's
chokker with hard links. I *really* don't want to cp the contents ...)

BUT. If you really do want to break the mirror (as I might, just to see
what happens :-), then your best bet is to add a third disk, let it
sync, then fail it off and play with that disk.

As the others said, if you have a 0.9 or 1.0 superblock, your filesystem
starts in the same place as your partition, so if you delete the
superblock the partition becomes non-raid. But if your superblock is 1.1
or 1.2, then that won't work.

Cheers,
Wol