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Peter Wright wrote:
> On 21/01 10:48:50, Tino Schwarze wrote:
>> On Wed, Jan 21, 2009 at 02:08:31PM +0900, Peter Wright wrote:
>>>> An incremental backup will transfer changed data from the
>>>> previous full or incremental of a lower level.
>>> Can backuppc be configured to transfer changed data from the previous
>>> incremental of the *same* level, or would this require a patch?
>> Why would you want to do that? The previous incremental of the same
>> level is a lot older and you'd need to transfer a lot more changes.
>
> Take my words in the context of responding to Adam - though perhaps I
> could have put it more clearly :).
>
> Adam stated that "An incremental backup will transfer changed data
> from the previous full or incremental of a lower level."
>
> What I was thinking is that if my highest priority was minimising
> bandwidth per backup, why shouldn't I be able to configure backuppc to
> *only* do incrementals and consider them all to be the same "level"?
Since "previous full or incremental of a lower level" is not the same as
"all incremental on the *same* level"... Each transfer would in effect
be compared to the previous full, which will get progressively worse
(based on your goal of bandwidth usage minimisation).
> But I suspect I've probably misunderstood one or more key backuppc
> principles, especially re: what the "levels" really mean.
>
>> In default configuration (IIRC), your backups with weekly full would
>> look like this:
> [ snip description ]
>> The second level-1 incremental will transfer all changes since the
>> full backup.
>
> Thanks for the clarification - that was how I thought it worked, but
> it's good to make sure.
>
> My key issue is that if I'm interested in bandwidth minimisation above
> all else, why would I want to do anything other than
> incremental-since-the-most-recent-previous-incremental, regardless of
> the "level" concept?
Actually, it is the opposite. If bandwidth minimisation is your only
concern, then every backup should be a full..... Since each backup will
only transfer the changed portions of existing files, or new files,
compared to the previous (full) backup. This will minimise your
bandwidth usage.
> As I understand Holger's earlier response, the major (only?) downside
> is the cost of building the backup view - and I can certainly see how
> that'd become significant after a while.
>
> I suspect I've got my brain too hooked into the rsnapshot model
> (http://www.rsnapshot.org/) and I'm not quite understanding the
> different philosophy of backuppc.
I presume you were doing a "full" backup each and every time using
rsnapshot... ie, you didn't tell rsync to ignore files based on the
modification date/time. So rsnapshot doesn't have any concept of
full/incremental, since every backup is a full. You just need to carry
that idea forward, and ignore the additional "feature" of incremental
backups that backuppc offers.
Hope that helps...
Personally, I have a backuppc which never deletes a backup, it currently
has over 800 backups for each host. I started with your mistake, of
doing a full + forever incremental, but once I realised my error, now do
a full, 3 incrementals, and another full, etc... The incremental's are
done to reduce the load (and hence time) on the machines being backed up.
Regards,
Adam
- --
Adam Goryachev
Website Managers
www.websitemanagers.com.au
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