Re: MDRaid Rollback

[Roman Mamedov <rm@romanrm.net>]

On Wed, 24 Mar 2021 14:44:07 +0000
Andy Smith <andy@strugglers.net> wrote:

> The default metadata version (1.2) is placed at the start of an
> array, so even if zeroed this will prevent the array member being
> used as the filesystem that is on top of it.
> ...
> Finally, if you are on superblock versions 1.1 or 1.2 you may be
> able to work out the offset into the device and use a loop device to
> skip that, so treating it as a normal filesystem:
> 
>     https://raid.wiki.kernel.org/index.php/RAID_superblock_formats#The_version-1_Superblock_Format

Also could delete the partition and recreate it with the new starting offset,
matching the offset for actual data. Recently I've migrated a couple of disks
off LVM in this manner.

Or if the entire disk was used as an array member, then create a brand new
partition table on it, with a single partition of the required offset.

sfdisk is helpful for dumping partitions into a text file ("-d"), which can
then be edited and restored to the device with "sfdisk /dev/disk < file".

All of this is likely more complex if you have to use GPT.

-- 
With respect,
Roman