Gene Horodecki wrote:
> Hi there.. Maybe not an important question, but it's bugging me. I must be
> missing something. If there is really only ever one pool of unique files
> in the BackupPC storage area, what's the point of having both full and
> incremental backups?
>
> In my current setup, i have a full once a week with incrementals every
> other day because files are duplicated and it saves space. But with the
> awesome efficiences offered by BackupPC, it seems to me incremental/full
> becomes a mute point and a person might as well do an incremental every day
> perminently, or a full every day if you're worried about missing files with
> the incremental.. Either way, it's going to use the same amount of storage
> is it not?
The difference is just in time, cpu use, and network bandwidth for the
backup runs to complete. With tar and smb methods, all files are
transfered on a full run and only ones with new timestamps on
incrementals. All duplicate content is discarded by the pooling
mechanism after the transfer. With rsync, fulls work by comparing the
contents of the previous full with the remote by exchanging block
checksums to avoid sending matching content. This takes time and CPU at
both ends but not a lot of bandwidth other than the changed content.
Rsync incrementals do the same but skip the content check on files where
the directory timestamp and length match the previous copy.
If you have the bandwidth and time for all backups to complete, there's
nothing wrong with doing fulls every night. Otherwise you would want to
set up a mix of fulls and incrementals so different machines do fulls on
different nights. With tar and smb incrementals you may miss files that
have been copied or moved in ways that preserves an old timestamp and
rsync becomes less efficient as you get farther away from a full run.
--
Les Mikesell
[EMAIL PROTECTED]
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