[Beowulf] OT: recoverable optical media archive format?

Kilian CAVALOTTI kilian.cavalotti.work at gmail.com
Wed Jun 9 03:33:16 EDT 2010


On Tue, Jun 8, 2010 at 8:05 PM, Michael Di Domenico
<mdidomenico4 at gmail.com> wrote:
> Not that it's elegant, the first thing that pops to mind is using
> 'split' to chunk the file into many little bits and then md5 each bit

While this may let you know that a file has been corrupted, it won't
help recovering that file.

Some compression algorithms, which may be considered as storage
algorithms if you turn compression off, have options to create
recovery records. For instance, in the RAR format
(http://en.wikipedia.org/wiki/RAR), you can choose how much redundant
data you want to include in your archive (whose size will be increased
accordingly).

Excerpt from Alexander Roshal's rar user's manual:

"""
    rr[N]   Add data recovery record. Optionally, redundant information
            (recovery record) may be added to an archive. This will cause
            a small increase of the archive size and helps to recover
            archived files in case of floppy disk failure or data losses of
            any other kind. A recovery record contains up to 524288 recovery
            sectors. The number of sectors may be specified directly in the
            'rr' command (N = 1, 2 .. 524288) or, if it is not specified by
            the user, it will be selected automatically according to the
            archive size: a size of the recovery information will be about
            1% of the total archive size, usually allowing the recovery of
            up to 0.6% of the total archive size of continuously damaged data.

            It is also possible to specify the recovery record size in
            percent to the archive size. Just append the percent character
            to the command parameter. For example:

            rar rr3% arcname

            If data is damaged continuously, then each rr-sector helps to
            recover 512 bytes of damaged information. This value may be
            lower in cases of multiple damage.
"""

Cheers,
-- 
Kilian
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