Hi, Carl W. Soderstrom wrote on 2018-06-14 16:03:24 -0400 [Re: [BackupPC-users] Slow local backup]: > On 06/14 03:38 , Bowie Bailey wrote: > > On 6/14/2018 3:27 PM, Michael Stowe wrote: > > > Why are you using rsyncd over the loopback instead of ??? rsync? > > > > Mainly because that's the way all of my other clients are being backed > > up [...] > > I've always used tar for local backups. The advantage of rsync is greater in > bandwidth-constrained environments because it saves moving whole files over > the network. However, if the file needs to be read anyway to see if anything > has changed, then nothing is saved because the local machine is the same as > the remote machine.
well, mostly true. You still save copying large amounts of data from one process address space to another and possible some context switches. While that may not make rsync *faster* than tar on local backups, it might mean it's not much slower. It probably depends on your setup. And it probably has low enough impact not to worry about it. > I may be incorrect about some of my understanding here, I know rsync does a > few things which tar does not, but which slip my brain at the moment. tar only has a single timestamp to go by (for incremental backups), rsync has a complete file list. This means that tar will miss *all file deletions* - deleted files will continue to show up in your backups until the next full - as well as renamed or moved files and probably files created with an old timestamp (eg. 'touch --date', 'touch --reference', 'cp -p', 'unzip', 'tar x' etc.). This is important! *tar incrementals will not be exact snapshots*! Well, neither will rsync backups, unless you use a snapshot of the underlying file system (or your file system is quiescent during backup), but that's a different matter. How much effort you should put into getting exact backups depends on what you expect to get out of them. * For restoring the occasional bunch of files from a backup because someone deleted them or messed them up, tar backups are fine. * For restoring a complete file system in the state it was in before it failed, you will want rsync backups, possibly with snapshots (depending on the type of activity on the file system). * If you're not sure what you need, but want to avoid surprises, go with rsync ;-). > Also, some uses of rsync may be more efficient than this by only checking > timestamps. That sounds like rsync incrementals. They will catch * files not in the backup, * files with modified timestamps, and * files with different size, even if the timestamp appears unchanged. Only rsync fulls will actually read all files. My recommendation for local backups: rsync(d). Hope that helps. Regards, Holger ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net List: https://lists.sourceforge.net/lists/listinfo/backuppc-users Wiki: http://backuppc.wiki.sourceforge.net Project: http://backuppc.sourceforge.net/
