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

From: Frank Crawford
Subject: Re: [rdiff-backup-users] Incredibly slow i/o to NAS server
Date: Mon, 05 Dec 2016 21:01:08 +1100

On Sun, 2016-12-04 at 08:58 -0600, Robert Nichols wrote:
On 12/03/2016 09:32 PM, Andrea Bolandrina wrote:
Bob - yes, lots of files under /mnt/vms/docker/ have more than one hard link. I might try your suggestion (--no-compare-inode) if I run into trouble again. 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 up. 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. And of course there is the issue I mentioned with huge numbers of zero-diff increment files if the device number changes, and that device number can vary randomly when LVM and/or encrypted devices are involved. My only solution for that is a script that refuses to run the backup if the device numbers don't match what was previously recorded. I really want to look into SafeKeep <http://safekeep.sourceforge.net/> as an alternative, but I haven't had a chance to do that.
However, SafeKeep uses rdiff-backup under the covers, it is just we have spent a lot of time trying to optimise the options that we pass to rdiff-backup.


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