Re: How to replace a failing device

[Roman Mamedov <rm@romanrm.net>]

On Wed, 2 Nov 2022 00:32:32 +0500
Roman Mamedov <rm@romanrm.net> wrote:

Some afterthoughts...

> Remove this cryptsdc2 from the FS (btrfs dev remove), stop the crypto device,
> wipe sdc2 entirely with wipefs.

That's not "entirely" of course, but just wiping the signatures is enough.

> After "ddrescue" manages to copy whatever it could, power-off and remove the
> old failing "sdd" from the system. Do not boot the main OS with both disks
> still plugged in. You can wipe the failing one later (after verifying the
> created copy is good) on some other PC, or booting into the same rescue system
> again.

After verifying it is good, you can enlarge the Btrfs' opinion of the
partition size on the copied 16TB device, see "btrfs resize devid:max ..."

> > $ sudo btrfs fi df /
> > Data, single: total=3.15TiB, used=2.74TiB
> > System, RAID1: total=32.00MiB, used=432.00KiB
> > Metadata, RAID1: total=110.00GiB, used=18.25GiB

^ A side note, this looks weird, as if at some point you had a ton of tiny
files, and then you removed them. If I'm not mistaken, running:

  btrfs fi balance -musage=80 ...

could gain you around 150 GB of usable disk space (as seen in df and
accessible for writing non-tiny files).

But of course do that only after the failing disk problem has been resolved.

And I vaguely remember that at some point the kernel may have started doing
this kind of cleanup automatically.

> > GlobalReserve, single: total=512.00MiB, used=0.00B

-- 
With respect,
Roman