Hi -
I have been looking at network transfer speeds and comparing them to the
rates reported for full backups.
The full backups use rsync, server is a Mac Xserve, client is an Ubuntu
Hardy machine. This is NOT the first backup of the machine. This machine is
also using checksum caching.
The web interface reports that my most recent full backup was done at a rate
of about 8MB/sec (pretty typical, give or take).
During the backup (which took about an hour) I was running network speed
tests with iperf. The tests where one-way, from the backup client to the
backup server. During this time the rates reported by iperf were always less
than 1MB/sec (e.g. 0.4Mbits/sec or 0.05 Mbytes/sec)! (Yes, I know that's
very slow - that's a part of the larger problem I'm trying to solve.)
Why the discrepancy?
If I naiively assume that a full backup (rsync+ssh XFER method) will
transfer ALL FILES to the server, then there is no way to understand the
discrepancy.
If, on the other hand, I assume that rsync is doing file comparisons on
both ends and transferring files as needed (i.e. those which are different
than those in the pool, or which are new), then the actual amount of data
transferred is less than the full amount (the web interface says its just
92MB new files). If so, then the rates I measure using iperf are closer to
what backuppc/rsync actually transferred (92MB/70 min = 0.02 MB/sec).
Is either of these cases correct, or is there another way to understand
this?
Will the same be true for a machine that does NOT use checksum caching?
Dan
--
Daniel J. Sperka, Ph. D.
UC Davis Center for Neuroscience
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