Based on this thread, is there any benefit in doing incremental backups when
using rsync?
It seems to me that full backup are vastly superior to incremental ones
because:
* They do use existing data available on the server and do not use more
bandwidth than incremental backups
* A partial backup is saved if the backup fails during the transfer
* Because of the linking done, they do not use more space on the server than
incremental backups
* They are self dependant and do not rely on other backups
Is this correct?
Thanks
Raphael
On Sat, Sep 6, 2008 at 9:20 PM, Holger Parplies <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Stephen Vaughan wrote on 2008-09-06 19:11:08 +1000 [Re: [BackupPC-users]
> Full vs. Incremental (was: Backup through slow line?)]:
> > What about with multiple full backups, say your full backup is 50gig and
> you
> > do a full backup once a week, will mean each full backup will use 50gigs
> of
> > space? Or does the pool do some other linking between the data contained
> in
> > each full backup?
>
> pooling also works for full backups. Why shouldn't it?
>
> Remember: if you've got a file containing just the word "foo" (or - more
> usefully - any other content) and store it in multiple locations, on
> different
> machines, in different shares, multiply within a share, and take as many
> backups of all of those machines and shares as you want, you will still
> only
> have one file in the pool to which all of those occurrences are linked -
> providing maximum link count permits. Only when you reach
> $Conf{HardLinkMax} -
> 31999 by default - occurrences, will a copy of the pool file be created for
> the next $Conf{HardLinkMax} occurrences. For reference, 31999 weeks is over
> 613 years, so if you have no duplication within your data or across
> servers,
> you probably won't be around to see that happen ;-).
>
> What will *not* be shared between full (or incremental) backups is the
> directory structure for the pc/<backupnum> trees. The directory tree as
> such
> is identical in a full and an incremental backup, but a full backup
> contains
> directory entries for all existing files, an incremental only for changed
> files. A directory with 1000 entries occupies more disk space than an empty
> directory. This means that a full backup will in fact use more space than
> an
> incremental - typically only slightly more, but if you have very short
> files
> with very long names, that might be different. Compare the output of 'df'
> and
> 'df -i' (on the systems you are backing up, not the pool file system!) or
> the
> BackupPC stats to get a rough idea of your average file size before or
> after
> compression, considering or not considering pooling (actually, you're
> interested in the size of compressed new files). Depending on file system
> and
> mount options, storage allocation for files and directories usually happens
> in multiples of file system blocks (usually something like 1KB or 4KB),
> which
> is also true for the pool, so even an "empty" directory in an incremental
> may
> take up 4KB of disk space (because it actually contains entries for '.' and
> '..' - empty *files* should *not* take up disk space except for the
> directory
> entry).
>
> To summarize, it depends on your setup, and you probably don't need to
> worry
> about it :-).
>
> Regards,
> Holger
>
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--
Raphael Alla
Alphalog Calédonie
Mitija Australia
+61 4 15 678 576
+687 78 86 86
http://www.mitija.com
http://www.alphalog.nc
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