Re: [rdiff-backup-users] How to speed up rdiff-backup

[Ben Escoto]

>>>>> dean gaudet <address@hidden>
>>>>> wrote the following on Fri, 14 Oct 2005 19:58:32 -0700 (PDT)
> On Fri, 14 Oct 2005, Carsten Lorenz wrote:
> 
> > Has anyone hints how to speedup rdiff-backup?
> 
> i just had a random idea while reading one of the other threads...
> 
> maybe fsync is the culprit for the slow initial backups (compared to 
> rsync) ... it would also slow down increments, but assuming a typical rate 
> of file change that wouldn't be as noticable.
> 
> what would probably be telling is to get some "strace -r -T" output during 
> an initial backup and see just where it's spending its time.  i tend to 
> take such output and run it through sort -t\< -k 2,2 ... which would sort 
> on the <n.nnnn> syscall timings... look for the worst culprits then work 
> backwards to figure out wtf rdiff-backup was trying to do when it hit 
> those worst cases... but if you send me some output i can do the data 
> mining.

rdiff-backup doesn't fsync on an initial backup, except for one global
sync() at the end before it writes the current_mirror file.  The
fsync()ing is only when doing incremental backups so it can regress if
necessary.  But on an initial backup there is nothing to regress to so
fsyncing isn't necessary.

The strace stuff is interesting, but you may want to try increasing
those bufsizes first, since it would just take a few seconds and you
might see an improvement.


-- 
Ben Escoto

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