Re: [Bug 12732] New: hard links can cause rsync to block or to silently skip files

[Hansjoerg Lipp via rsync]

Am 05.04.2017 um 22:05 schrieb L A Walsh via rsync:
>I ran rsync 3.1.1 for over a year to help generate
> snapshots.  I can't say if it copied all the files or not, as
> it was backing up a large "/home" partition, BUT, it never hung.
> It did take 45min to a few hours to do the compare, but it
> was comparing a large amount of data (>750G) w/a snapshot
> (another 750G) to dump diffs to a third, and my /home partion
> has a *very* large number of hard links.

I've been using rsync for many years and it works fine most of the time.
I'm not sure if all of the occasional hangs have the same reason, these
are really hard to track down as they usually occur during large
transfers (e.g. when synchronizing large backup disks). That's why I was
happy that I could find a small test case which triggers this problem.

Does your rsync hang after the sequence of commands described in section
"How to reproduce (2)"?

>> Latest test on openSUSE 42.2 (x86_64) on ext4 + on nfs with
>>   
> 
>Ah...  I'd suspect nfs...
>  Why are you using nfs?

In order to find out if there is a difference when using another file
system type. The most recent tests were on ext4 and on nfs
(independently), older tests were on at least ext3 and xfs. IIRC I only
tested on different OpenSUSE and Debian versions on x86_64 systems, though.

>Just checked my /home partition.
>find shows 9295431 names (of any type), but du shows
> (using du --inodes) shows 4407458 inodes.  That means over
> half of the filenames are hard linked.  While my home
> partition takes up 60% more space now, even cutting
> those counts in half would still a large number of
> hard links -- and rsync didn't crash doing an
> rsync of the partition to an empty one, but first comparing
> to a previous snapshot (the empty partition ended up
> with differences between the main partition & the snapshot.

Probably using different options? Can this be some sort of Heisenbug,
nobody can reproduce? Do the two sequences of shell commands work for
you as expected? Please note that both rsync commands in the mail
generated by bugzilla are split into two lines (each): Both rsync
commands should read
   rsync PARAMS DIRS >> XXX.log 2>&1

Kind regards,
Hansjoerg

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Re: [Bug 12732] New: hard links can cause rsync to block or to silently skip files

[L A Walsh via rsync]

just subscribed for rsync-qa from bugzilla via rsync wrote:

Hard link handling seems to be broken when using "rsync -aH --compare-dest". I
found two possible scenarios:

1) rsync completes without error message and exit code 0, although some files
are missing from the backup
2) rsync blocks and must be interrupted/killed


Further information
===

This problem exists at least for rsync versions 3.1.0, 3.1.1, and 3.1.2 for
different Linux varieties using various file systems:
https://lists.samba.org/archive/rsync/2015-April/030092.html
  

---

   I ran rsync 3.1.1 for over a year to help generate
snapshots.  I can't say if it copied all the files or not, as
it was backing up a large "/home" partition, BUT, it never hung.
It did take 45min to a few hours to do the compare, but it
was comparing a large amount of data (>750G) w/a snapshot
(another 750G) to dump diffs to a third, and my /home partion
has a *very* large number of hard links.

   So I know that hardlinks are handled 'fine' on comparing
'xfs' to 'xfs'. 

Latest test on openSUSE 42.2 (x86_64) on ext4 + on nfs with
  


   Ah...  I'd suspect nfs...
  
   Why are you using nfs?  rsync was designed to compare

against local file systems.  You should try running rsync
directly from the nfs-host machine to the client and bypassing
NFS.  I.e. -- you need to bypass NFS, since local->local
with hardlinks works.

   Just checked my /home partition.
   find shows 9295431 names (of any type), but du shows
(using du --inodes) shows 4407458 inodes.  That means over
half of the filenames are hard linked.  While my home
partition takes up 60% more space now, even cutting
those counts in half would still a large number of
hard links -- and rsync didn't crash doing an
rsync of the partition to an empty one, but first comparing
to a previous snapshot (the empty partition ended up
with differences between the main partition & the snapshot.

   I'd remove NFS...




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