Re: How to replace a failing device

[Roman Mamedov <rm@romanrm.net>]

On Wed, 02 Nov 2022 20:51:11 -0700
Matt Huszagh <huszaghmatt@gmail.com> wrote:

> 99.99% data rescued with 2 bad sectors. Since I didn't have any trouble
> backing up recent data, I'm optimistic I haven't lost anything of value.

If your backup is incremental and only copies modified files, you can ensure
all other files are also readable by recursively reading them:

  find -type f -print0 | xargs -0 cat > /dev/null

...for a kind of manual scrub. Unless you had nocow/nodatasum files in there,
any damaged ones will return a read error thanks to Btrfs checksums.

Or maybe you could check if Btrfs scrub has also stopped hanging, given there
are no disk-level unreadable sectors anymore. (And after you have also
upgraded the kernel).

> I'm investigating RAID configurations (probably RAID10) as a way to make
> the process of replacing faulty drives somewhat smoother in the
> future. If you have any opinions on this would be curious to hear
> them. I'll probably also setup a periodic systemd service to run
> smartctl and detect issues (hopefully) earlier.

Btrfs currently does not seem to be famous for smooth disk replacements
unfortunately, even if you would use RAID.

I would suggest keeping up with the good backup schedule, and then rather than
using the Btrfs "single" profile stretched across devices, switch to MergerFS.
That way any disaster on a particular disk leaves other disks and their
independent filesystems completely unaffected.

-- 
With respect,
Roman