Re: [Dar-support] Multiple slices on LTO6 tape

[Denis C. <dar...@fr...>]

Le 09/06/2022 à 20:54, Denis Corbin a écrit :
[...]

> If I  can ask you for future improvement, I would suggest to modify 
> the code to allow reading of individual slices (i.e. tapes ) even if
> the content is not consistent (i..e the slices 2 and more will have
> some file on the boundary but the listing still can be done after
> ignoring this - when finding next escape sequences.

amending what I writings:

> 
> you are not the first to ask for that, but this is not possible by 
> design. Dar is structured in layers which are very independent from
> each others
> (slicing/caching/encryption/tape-marking/compression/sparse-file 
> detection/and so on). On top of them, the backup structure, i.e. the 
> metadata and file's data is completely ignorant of what is
> underneath.
> 
> Such software architecture allowed a lot of feature additions over
> time (thing that only compression and slicing were available in dar
> 1.0.0 twenty years ago). Having such architecture of independents
> classes is also one of the reasons that lead dar to be so robust and
> to have so little bugs. Breaking this would require to remove
> dar_xform and dar_slave, backup merging and backup repairing, at the
> very least.
> 
> [...]

there is maybe the possibility to not touch this layered structure and
archive format, to somehow achieve this same goal: by mean of isolated
catalogue with probable minor modification.

However files spanning between successive slices would not be restorable
doing that way, they would even be filtered out to keep a per slice
operation.

But if by "reading" you just mean listing the content per slice, there
is already the possibility to do this:

	dar -l <backup> -Tslice

last, thanks to the lax mode you can, in a way operate data per slice
(listing/restoring/...), but that's not a straight forward solution and
stays a last resort option.

Cheers,
Denis