Re: change timestamps of backups?

On 22/04/2021 08:01, griffin tucker wrote:
> I've tried using deduplication, but only get about 6gb savings per 30gb.
>
> I intend on using squashfs on top of rdiff-backup, btrfs is just being
> used temporarily.
>
> On Thu, 22 Apr 2021 at 16:41, Dominic Raferd <[email protected]> wrote:
>> On 22/04/2021 07:03, griffin tucker wrote:
>>> i have a collection of the last 5 monthly dumps of various wikis from
>>> dumps.wikimedia.org
>>>
>>> each dump has numbered directories in the format 20210501, 20210401,
>>> 20210301, etc.
>>>
>>> all the filenames in these directories remain the same with each
>>> wiki's dump, with the exception of enwiki
>>>
>>> other than enwiki, these range from about 30gb to about 370gb
>>> uncompressed with each successive dump
>>>
>>> enwiki, the main english wikipedia, has mostly the same named files,
>>> but has the pages-meta-history.xml file split up into various 1-55gb
>>> compressed files (mostly 1-2gb) making a total of about 700gb
>>> compressed (disregarding redundant files)
>>>
>>> i'm not sure how big enwiki is uncompressed, but could be close to
>>> 25tb. i haven't figured out how i could make rdiff-backup more
>>> efficient with these files, aside from a script to merge each
>>> metahistory file into a single huge >100gb file and then running
>>> rdiff-backup, and then splitting the file back into their separate
>>> files with an index after restoring
>>>
>>> i'm using btrfs zstd:15 to store the files uncompressed, however i
>>> don't have enough storage to store enwiki uncompressed, zstd
>>> compression just isn't that good, even at maximum - i've used xz
>>> compression which attains much better rates of compression for other
>>> wikis but that isn't exactly seamless (experiments with fuse failed)
>>>
>>> so, to save space, i thought i would use rdiff-backup so that it would
>>> only store the differences between dumps, and it works very well in
>>> initial tests, however, if i run the reverse incremental backups one
>>> after the other today, they would be dated today, rather than
>>> 20210501, 20210401, etc. which isn't informative
>>>
>>> if i could add a comment next to each datetime stamp, this would be
>>> useful, otherwise i'll have to keep a separate index, which isn't a
>>> huge problem, i just thought i'd ask if i could change the datetime
>>> stamps before i write such a script
>>>
>>> On Thu, 22 Apr 2021 at 15:19, Eric Lavarde <[email protected]> wrote:
>>>> Hi Griffin,
>>>>
>>>> On 22/04/2021 06:39, griffin tucker wrote:
>>>>> is there a way to change the timestamps of the backups?
>>>> no
>>>>
>>>>> or perhaps replace the timestamps with a unique name?
>>>> no
>>>>
>>>>> would this cause a faulty restore or a damaged backup?
>>>> yes, rdiff-backup makes a lot of date/time comparaisons so the timestamp
>>>> is meaningful.
>>>>
>>>> What are you trying to do?
>>>>
>>>> KR, Eric
>> Since you are already using btrfs, have you considered using
>> deduplication? Likely to work better if you store uncompressed.
>>
In your scenario I would expect deduplication to give big savings if you 
store uncompressed. If not, YMMV. (I tried with rdiff-backup on btrfs + 
deduplication a few years ago but found it all a bit scary and retreated 
to ext4.)