UFS dump bigger than expected

[Andrea Venturoli]

Hello.

I've got a problem with an UFS filesystem: dump produces a file which is 
bigger than I expect.

# freebsd-version -ku
11.3-RELEASE-p10
11.3-RELEASE-p10
# uname -m
amd64

# df -h -t ufs|grep usr
/dev/mirror/gm0d    242G    199G     24G    89%    /usr

# cd /usr/
# du -x -d 0 -h
182G	.
# du -x -d 0 -n -h
9.2G    .

# /sbin/dump -0 -a -f /data/dumps/usr.dump -L -h 0 -u /usr
   DUMP: Date of this level 0 dump: Tue Jul 14 20:00:14 2020
   DUMP: Date of last level 0 dump: the epoch
   DUMP: Dumping snapshot of /dev/mirror/gm0d (/usr) to /data/dumps/usr.dump
   DUMP: mapping (Pass I) [regular files]
   DUMP: mapping (Pass II) [directories]
   DUMP: estimated 27584621 tape blocks.
   DUMP: dumping (Pass III) [directories]
   DUMP: dumping (Pass IV) [regular files]
   DUMP: 4.18% done, finished in 1:54 at Tue Jul 14 22:02:57 2020
   DUMP: 9.36% done, finished in 1:36 at Tue Jul 14 21:50:15 2020
   DUMP: 16.19% done, finished in 1:17 at Tue Jul 14 21:36:01 2020
   DUMP: 27.59% done, finished in 0:52 at Tue Jul 14 21:15:51 2020
   DUMP: 43.59% done, finished in 0:32 at Tue Jul 14 21:00:43 2020
   DUMP: 59.13% done, finished in 0:20 at Tue Jul 14 20:54:06 2020
   DUMP: 68.72% done, finished in 0:15 at Tue Jul 14 20:54:17 2020
   DUMP: 86.52% done, finished in 0:06 at Tue Jul 14 20:49:35 2020
   DUMP: 96.40% done, finished in 0:01 at Tue Jul 14 20:50:02 2020
   DUMP: DUMP: 27589206 tape blocks on 1 volume
   DUMP: finished in 2797 seconds, throughput 9863 KBytes/sec
   DUMP: level 0 dump on Tue Jul 14 20:00:14 2020
   DUMP: Closing /data/dumps/usr.dump
   DUMP: DUMP IS DONE

#ls -lh /data/dumps
total 27596000
-rw-r--r--  1 root  wheel    26G Jul 14 20:49 usr.dump



So, resuming, there's 182GB or 199GB of data here, but only 9.2GB of 
this should be dumped; the rest has the "nodump" flags active.
However I end up with 26GB of dump!

This machine has been there for something like five years and dump has 
always worked properly.

The only thing I came up with, while searching the web, 
is:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=111782
but this is a little different.

Any hint?

  bye & Thanks
	av.