partclone.ext4 twirls forever when working on an unmounted RAID partition

[Kevin O'Gorman]

I'm trying to clone an EXT4 partition on a Linux software RAID

I'm using the command line
  partclone.ext4 --clone --source=/dev/md1p1 --output=testout

when the relevant part of 'lsblk' output is
  sda 8:0 0 16.4T 0 disk
  └─md1 9:1 0 32.8T 0 raid5
    └─md1p1 259:0 0 32.8T 0 part
  sdb 8:16 0 16.4T 0 disk
  └─md1 9:1 0 32.8T 0 raid5
    └─md1p1 259:0 0 32.8T 0 part
  sdc 8:32 0 16.4T 0 disk
  └─md1 9:1 0 32.8T 0 raid5
    └─md1p1 259:0 0 32.8T 0 part

This has resulted in partclone.ext4 running for what I expect to be forever
because not a single byte has been written to 'testout', and it has been running for about 3 hours.
I tried it overnight once before, with the same result.

There was a little bit of output on stdout:
  root@plato-f:/mnt/18tc# time partclone.ext4 --clone --source=/dev/md1p1 --output=testout
  Partclone v0.3.13 http://partclone.org
  Starting to clone device (/dev/md1p1) to image (testout)
  Reading Super Block
  Calculating bitmap... Please wait...
  Elapsed: 00:02:11, Remaining: 00:00:00, Completed: 100.00%
  Total Time: 00:02:11, 100.00% completed!
and not a bit more.

Top(1) shows partclone.ext4 using 1.0 CPUs (of the available 32); this machine uses two Xeon chips.

There does not seem to be anything wrong with the RAID. I just now stopped partclone and remounted
the raid as usual, and I can see the usual files and directories in it. Moreover, I have been able to
use tar(1) and dar(1) on it previously, but I was really hoping for a better compression result.

The relevant line in /etc/fstab is
  UUID=625c7324-0102-43f8-9120-680ad6ad82c3 /raidp xt4 nofail,discard,noatime,acl 0 2

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: partclone 0.3.13+dfsg-4
Uname: Linux 6.0.12-76060012-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.27
Architecture: amd64
CasperMD5CheckResult: skip
Date: Tue Jul 9 16:24:53 2024
SourcePackage: partclone
UpgradeStatus: Upgraded to focal on 2022-05-13 (788 days ago)
modified.conffile..etc.default.apport:
 # set this to 0 to disable apport, or to 1 to enable it
 # you can temporarily override this with
 # sudo service apport start force_start=1
 enabled=0
mtime.conffile..etc.default.apport: 2017-05-02T14:12:29.908000