First off, I'm a happy user of BackupPC; I'm only posting because I have
an architecture question resulting in bad performance that I'm hoping
someone can answer.
I have a need to back up Windows clients. I got smb-based backups
working very well, or so I thought -- no matter what I tried, I couldn't
get some files backed up, even though the backuppc user was in the
Administrators group and I had run icacls to grant backuppc full file
rights. So I went through the trouble of setting up rsyncd and now I'm
backing up every file without an issue, except that things are moving
VERY slowly, even for new files that haven't been backed up before.
With smb, which used smbclient to do the transfers, I was seeing
transfer speeds of 40-65MB/s over a gigabit network -- with rsync-based
backups, I am seeing about 6MB/s, ten times slower.
I profiled File::RsyncP which is what BackupPC_dump appears to be using,
and found this troubling report after a profile time of one day:
time elapsed (wall): 86034.3727
time running program: 85959.5328 (99.91%)
time profiling (est.): 74.7665 (0.09%)
%Time Sec. #calls sec/call F name
83.30 71605.7838 913708 0.078368 ? File::RsyncP::pollChild
15.98 13737.1191 261 52.632640 File::RsyncP::writeFlush
0.21 176.3028 121432 0.001452 File::RsyncP::getData
(snip)
As you can see, pollChild is called a ridiculously large number of
times, which is eating up nearly 70% of the CPU time trying to do a
backup. This is extremely inefficient and completely explains why my
backups are taking so long over rsync (the CPU spends most of it's time
in pollChild).
So, my questions are:
- Is there a reason BackupPC needs to emulate rsync through File::RsyncP
instead of just using rsync itself?
- If not, is anyone maintaining File::RsyncP who can optimize that code
and/or redesign it?
Thanks in advance for any advice.
--
Jim Leonard (trixter AT oldskool DOT org) http://www.oldskool.org/
Help our electronic games project: http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
A child borne of the home computer wars: http://trixter.wordpress.com/
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