[Dar-support] to par or not to par...

[Gour <go...@at...>]

Hello,

TL;DR: The question is whether to use par2 or not with Dar while backing
up to RDX cartridges/drives.

being in the position to plan moving away from LTO(2)/tapes techology
where I mostly used Amanda software with some periods spent with Bacula
to RDX cartridges connected to external drive via USB3, dar is very
natural option.

However, there are several new 'remote encrypted deduplicated backup'
apps available and I have tried few of them in last few days...

1) bup (https://github.com/bup/bup) with which I could achieve ~16-17
MB/s when testing with sample data of ~70GB.

My machine was responsive and cpu was not very hot.

The problem is that after reading post comparing few of such tools
(http://librelist.com/browser/attic/2015/3/31/comparison-of-attic-vs-bup-vs-obnam/#38efeaa8ec969ac6cd5686352b10ad53)
but seems to be very slow whne restoring.

Moreover, it still does not have (it's in dev branch atm) capability to
delete old snapshots.

Next app I did test was:

2) restic (https://restic.github.io/) which performs well (~50MB/s),
does encryption, deduplication etc., but my machine was under heavy load
and almost non-responsive at cpu temperature did skyrocket from idle's
50C to 95C. :-(

Iow, restic works too well. :-)

In the attemt to eliminate problems with system overload I did try
another app:

3) Borg (https://github.com/borgbackup/borg) which has similar features
like 1) & 2), but it's quicker (~28MB/s), system was responsive during
backup and cpu temp was around 65C which is similar to e.g. bup.

Now, it's time to compare all of them with Dar and wonder what do they
provide in features/performance over it?

To me (uninititated), it looks that major feature is deduplication which
is missing in Dar.

Otherwise, Dar does compression, encryption, it can do remote backups
(although I am happy with just backing up to external drive). Moreover
Dar does not halt my machine during backup nor it fries my poor cpu at
95C.

The only gotcha I've encoutnered while testing Dar was/is that using
par2 is either too slow with single slice or not so slow but produces
large number of parity archives.

However, none of the above referenced tools (except bup) uses parity
archives which can be even more problematic considering they do
deduplication and in the case of some bitrotting the damage might be
bigger than with Dar.

So, my question is whether you recommend to use par2 parity archives
with Dar or is Dar's design and capability to cope with media errors
still good enough or on par with the above backup apps in which case it
makes it clear winner above the rest?


Sincerely,
Gour

-- 
Even a man of knowledge acts according to his own nature, for 
everyone follows the nature he has acquired from the three modes. 
What can repression accomplish?