Cesar Kawar wrote at about 10:08:10 +0100 on Friday, March 11, 2011:
 > 
 > 
 > El 11/03/2011, a las 08:04, hansbkk AT gmail DOT com escribió:
 > 
 > > On Fri, Mar 11, 2011 at 10:56 AM, Rob Poe <rob AT poeweb DOT com> wrote:
 > >> I'm using RSYNC to do backups of 2 BPC servers.  It works swimmingly, you 
 > >> plug the USB drive into the BPC server, it auto-mounts, emails that it's 
 > >> starting, does an RSYNC dump (with delete), flushes the buffers, 
 > >> dismounts and emails.
 > > 
 > > Sounds great Rob, would you be willing to post the script?
 > > 
 > > Rsync'ing is all fine and good until your hardlinked filesystem (I
 > > don't know the proper term for it, as opposed to the pool") gets "too
 > > big". It's a RAM issue, and an unavoidable consequence of rsync's
 > > architecture - I'm not faulting rsync mind you the kind of filesystem
 > > that BPC (and rdiff/rsnapshot etc) build over time is a pretty extreme
 > > outlier case.
 > > 
 > That is not a problem anymore with latests versions of rsync. I've been 
 > using this technique for a year now with a cpool of almost 1Tb with no 
 > problems.
 > 
 > Don't expect it to run on a celeron machine as it requieres big processors. 
 > Rsyncing 1Tb of compressed hardlinked data to a new filesystem is a very cpu 
 > intensive task. But it does not leak memory as before. You can relay on 
 > rsync to mantain a usb disk for off-site bakups.

I think rsync uses little if any cpu -- after all, it doesn't do much
other than do delta file comparisons and some md4/md5
checksums. All much more rate-limited by network bandwidth and disk
i/o.

I was under the impression that the slowdown, is due to the need to
build (and check) lists of hardlinks which is memory
constrained. Maybe when the list gets really long, cpu power is needed
to build/sort/lookup the list but I would think that if rsync were
written well, that this again would not be the rate limiting issue.

Would be interesting for someone to graph performance vs. amount of
memory and vs. cpu power/speed.

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