On Thu, May 6, 2010 at 5:53 PM, Les Mikesell <lesmikesell AT gmail DOT com>
wrote:
> On 5/6/2010 4:17 PM, Brian Mathis wrote:
>> I'm new to BackupPC and looking to keep long term snapshots. I've
>> been reading through the docs and I think the "levels" concept will do
>> what I want it to, but I still have some outstanding questions.
>>
>> I'm looking to use an 84 day cycle where:
>> - Day 0 is the full backup (level 0)
>> - Day 7, 14, 21 are incrementals relative to D0 (level 7)
>> - Day 28 is an incremental to D0 (level 1)
>> - Day 35, 42, 29 are incrementalss relative to D28 (level 7)
>> - Day 56 is an incremental to D28 (level 2)
>> - Day 63, 70, and 77 are incrementals relative to D56 (level 7)
>> - Day 84 is the next full backup (level 0)
>> There are no daily incrementals
>>
>> I think the above example means I need the config:
>> FullPeriod = 83.97
>> IncrPeriod = 6.97
>> IncrLevels = [7, 7, 7, 1, 7, 7, 7, 2, 7, 7, 7]
>>
>> Am I missing anything in that config?
>>
>> The next piece is incremental expiration. I would like to keep at
>> most six level 7 backups, but keep the level 0, 1, and 2 "forever". I
>> only see IncrKeepCnt which seems to be an all-or-nothing expiration
>> number that doesn't take levels into account. Is this possible?
>>
>> I expect each full backup to be large, and I'm hoping that this sort
>> of scheme will make the best use of disk space and file redundancy,
>> while keeping a long timeline of snapshots.
>>
>> Suggestions are welcome.
>
> Before you do something like this, be sure you understand how both
> pooling and rsync work. Backuppc will keep only copy of any file and
> will replace any others that have identical content with hardlinks.
> There will be next-to-no difference in disk space used by an incremental
> vs. full or a different level of incremental. Also, when you use rsync,
> there is not a big difference in network bandwidth use between fulls and
> incrementals because it only copies the differences anyway. Fulls do
> take much more time to complete, though, because even unchanged files
> are read each time for the comparison where incrementals skip any with
> identical timestamps and lengths.
>
> --
> Les Mikesell
> lesmikesell AT gmail DOT com
Good point. I've used rsync many times in the past and our current
custom solution uses the rsync hard link tricks to get the same kind
of advantages. I'm looking to get onto a less custom solution, hence
backuppc.
It sounds like you're saying I can probably achieve a similar effect
by doing a level 0 every 28 days and then doing weekly incrementals
relative to the level 0, and avoiding the multi-tiered level system I
outlined?
I was probably thinking that a full will always take up a full amount
of disk space, but you're right and I sort of forgot it all goes into
the pool and gets deduped anyway.
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