Hi, Carl Wilhelm Soderstrom wrote on 09.07.2007 at 08:12:18 [Re: [BackupPC-users] rsync incremental-only backups for eternity]: > On 07/09 08:22 , Rob Owens wrote: > > I see that the only difference between rsync "full" and rsync > > "incremental" backups is that "full" uses the --ignore-times option. > > Under what circumstances would this option be desirable? Seems to me > > that doing incremental backups forever would suffice, but maybe I'm > > missing something. What is the risk associated with only performing > > incremental backups with rsync?
http://sourceforge.net/mailarchive/message.php?msg_name=20070501024958.GM25826%40mail.parplies.de http://sourceforge.net/mailarchive/message.php?msg_name=20070615011832.GL25826%40mail.parplies.de > The way I tend to think of it (and I may be completely off base here) is > that 'fulls' are like what you get if you just run the 'rsync' tool from the > command line with no fancy options. 'Incrementals' are a faster way to do > things. I believe 'rsync's default mode of operation is actually incremental-type (i.e. optimize based on modification times). That makes sense for interactive operation, as you can decide what you need each time. '--ignore-times' is, in general, rarely needed, and it is an expensive operation, much like '-H' (which is also not default, even in '-a'). If you want to be absolutely sure you're making an exact copy, you need 'rsync -aH --ignore-times', but usually 'rsync -a' will do (and be much faster). Sometimes you might need to leave out '-o' and '-g' if you require copies with identical content but different ownership. As always, you need to know what you want before you can select the correct options to achieve it. If your interactive invocation does *not* do what you expect, you'll hopefully notice and correct it. For use as an automatic backup tool you want an invocation which produces an exact copy of your data under all circumstances - for every machine, whatever data your users happen to keep there, however they manipulate it. In addition, you likely won't notice anything going wrong until you need to restore the data and the restored data is not correct. As backups are commonly done frequently and with large data sets, it may be necessary to speed things up at an acceptable cost. Incremental backup strategies based on modification times are common enough. The drawbacks are basically known (if not always taken into account). With rsync, such a strategy *does* speed things up significantly, so it's natural to adopt a well known term and its well known implementation, even though rsync "full" backups in BackupPC already have almost all the benefits of conventional "incremental" backups (storage and bandwidth wise). > Always keep in mind tho that BackupPC is *not* using the rsync tool on the > server side. It's using the File::RsyncP Perl module. Meaning not all options it respects are visible in the remote rsync invocation, and not all rsync options are supported by File::RsyncP. The '--delete' options are examples of things the remote instance does not need to worry about. BackupPC will take note of deleted files although these options are not explicitly visible. > On 07/09 06:31 , Jean-Michel Beuken wrote: > > in theory, in the version 3.x of BackupPC, we can take incrementals of > > different levels ( $Conf{IncrLevels} )... > > but, my little experience shows that we don't gain a lot of time with > > high level (with rsync) worse some incr takes more > > times that the full :-( Some incrementals need to transfer more data than a full backup would in the same situation :-). Note also the cost of constructing a backup view which increases with the level of the backup. Regards, Holger ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ BackupPC-users mailing list BackupPC-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/backuppc-users http://backuppc.sourceforge.net/
