[Duplicity-talk] Have you considered using the "multiple data files" mode of par2?

[Jakob Bohm]

Dear Duplicity backup format designer,

According to the par2 man page (at least on Debian 12), the par2 command
has two distinct operating modes.  One mode creates one or more small
parity files for a single data file stored on an imperfect medium or
service.  The other, processes a group of N data files (such as
Duplicity volumes) to produce a few shared parity files.  This second
mode is described in the man page under the subheading "CREATING PAR2
FILES FOR MULTIPLE DATA FILES" .

Switching to the "multiple data files" mode constitutes a change in
the backup format and thus needs to be guarded with appropriate
compatibility logic in order to restore backups made with either
method, even from damaged storage (where par2 files are actually
needed) .  To keep a desired robustness level and a manageable temp
volume size on the client, it is probably necessary to set an internal
limit on the number of volumes for each par2 run .  For example if
that limit is 99, the temp volume needs to store about 100 times the
volume size even if not pipelining the creation of later volumes in
parallel with par2 processing and upload.

Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
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