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Re: [rdiff-backup-users] Incredibly slow i/o to NAS server

From: Robert Nichols
Subject: Re: [rdiff-backup-users] Incredibly slow i/o to NAS server
Date: Mon, 5 Dec 2016 15:26:38 -0600
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On 12/05/2016 09:28 AM, Joe Steele wrote:
On 12/4/2016 9:58 AM, Robert Nichols wrote:
On 12/03/2016 09:32 PM, Andrea Bolandrina wrote:
What problems does rdiff-backup have with hard linked content?
As far as I know hard links should be supported...

Supported?  Yes, but with plenty of bugs.  If links are added and
removed from a set, you can end up with two or more separate subsets
(i.e., what should be a set of 10 links to a single file becomes 3 files
with link counts of 3, 5, and 2), and the link arrangement in the
metadata files won't always match the link arrangement in the mirror.
The checksum is stored only for the first link in the collating
sequence.  If that first link gets deleted, the checksum is lost.  If a
link with a path that comes earlier in the collating sequence is added,
it sometimes does not inherit the checksum.  I have a massive and
time-consuming audit that I run after every backup session to patch that

Verification always complains about missing checksums for all the links
that do no have one stored.  I have to filter out all the verbose 2-line
messages for those from the verification report.

I believe the harlink problems you describe are identified in this bug report 
(that I submitted in 2009):


Attached to the report are patches to fix the issue.  Some distros (which I think 
include Debian, Ubuntu, & Suse) have since been including the patches as part 
of their packaging.

Those patches look like they address the problems with checksums being misplaced 
or lost, but they don't appear to have anything to do with what I see as the 
greater problem of sets of hard links being broken up and inconsistencies between 
the hard link counts in the metadata and the mirror.  I finally got rdiff-backup 
to build (needed a patch for librsync >= 1.0.0), so I can do some testing later.

Bob Nichols     "NOSPAM" is really part of my email address.
                Do NOT delete it.

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