Re: BackupPC 4.0 features - attribute file and backup storage

re to Jeffrey J. Kosowsky <backuppc@ko...> -	2011-03-02 15:59 
> If you are changing the appended rsync digest format for cpool
>    files using rsync, I think it might be helpful to also store the
>    uncompressed filesize in the digest There are several use cases
>    (including verifying rsync checksums where the filesize is required
>    to determine the blocksize) where I have needed to decompress the
>    entire file just to find out its size (and since I am in the pool
>    tree I don't have access to the attrib file to know its size).
> 


re to Jeffrey J. Kosowsky <backuppc@ko...> -	2011-03-03 16:40

> Alternatively, if you want the first time hack to work then you could
> make the pool file name equal to: <md5sum>_<SHA-256sum> which would
> still be smaller than SHA-512sum and I would wager that we are
> unlikely ever to start seeing lots of files with simultaneous
> collisions of the md5 and the SHA-256 checksums. In a sense, the
> SHA-256 checksum would act like a unique chain suffix and since it
> would always be there you never would have to actually decompress and
> compare the files to see if a chain is necessary. Plus you then would
> have two essentially independent checksums built into the file name.


i would propose to extend it to 
<MD5>_<SHA_256>_NULL_<uncompressed_FILESIZE>
by default

and an option for (if user enables it :)
<MD5>_<SHA256>_<SHA512>_<uncompressed_FILESIZE>
maybe somebody wants to to recalculate the SHA512 sums afterwards (in idle time?) - therefore the "NULL" in the default name above

indeed ... this would generate very long filenames: 

as for the name-length limit of 255
32_64_128_<filesize>
meaning there would be space left for 27 more characters (10^26) 

so we could also append Filesizes of ... uuh ... wait ... 
   10^12 - Terabyte
   10^15 - Petabyte
   10^18 - Exabyte ....
well ... very big files :)

Having all kinds of checksums and sizes already calculated - these information may be reused for custom user-scripts like
# integration testing of pool  using md5, sha256 AND sha512 :)
# appending .sha256 or sha512 files in archive-operations
# post-dump integrity tests on client  ...

Greetings 
Mike


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