Date: Tue, 01 Nov 2005 16:15:50 -0500 From: Chuck Swiger <cswiger@mac.com> To: user <user@dhp.com> Cc: freebsd-questions@freebsd.org Subject: Re: two quick conceptual questions RE: rsync (and rsyncing snapshots) Message-ID: <4367DB06.5030400@mac.com> In-Reply-To: <Pine.LNX.4.21.0511011528460.8180-100000@shell.dhp.com> References: <Pine.LNX.4.21.0511011528460.8180-100000@shell.dhp.com>
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user wrote: > First, how does rsync respond to, and perform, when the source filesystem > is under very heavy change ? If I have a filesystem that I want to rsync > up to a backup server, but that filesystem is _very busy_ with the > creation, destruction and changing of files, how well does rsync perform, > and how much does it interfere with the performance of the underlying > filesystem that it is sending up to the backup server ? rsync complains when the filesystem changes underneath it, but it will continue to run. On the other hand, rsync is not going to safely maintain the referential integrity of a complex file like a live database, but it's okay for most other things including mbox's. Rsync imposes a significant workload if you are syncronizing a large tree of stuff which changes a lot, but it's efficient considering the size of the task. > Related: it occurs to me that perhaps it would be better to snapshot the > filesystem, mount the snapshot, and then rsync the snapshot. On the other > hand, the filesystem is continuously altering the snapshot as files are > destroyed or changed ... so perhaps this does not gain anything. Is > rsyncing a snapshot of a busy filesystem always, ever or never easier than > rsyncing the busy filesystem itself ? rsync'ing a snapshot is a fine idea. > Finally, am I correct that there are _only two_ rsync comparison methods - > the default checksum method, and the --size-only method ? Am I correct > that rsync _always_ looks at the timestamp first, and then applies either > checksum or size comparison ONLY IF the timestamps are different ? No, rsync checks both timestamp and size or checksum. -- -Chuck
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