Re: [Bug-tar] [bug] multi-volume archive not compatible with --sparse

[Joerg Schilling]

Marek Marczykowski-Górecki <address@hidden> wrote:

> Hi,
>
> I've noticed that sparse file header can't be splitted across multiple archive
> volume. So if you try to make a multi-volume archive of a big sparse file
> (with a lot of holes), it can happen that a file header (list of the holes)
> will not fit on the same archive volume. Tar then continues such a header on
> the next volume, but *without any tar archive header*. If even second volume
> isn't enough, it looks like the header got truncated there and tar starts the
> file data (with a proper header this time) on the next volume.
> When you try to extract such a file from an archive, tar complains that the
> second volume doesn't look like tar archive. When you concatenate all the
> volumes and extract this archive, it will look better (apart from "tar:
> Skipping to next header" message), but the file will be broken.
>
> The worst thing here - tar pretends that the archive was successfully created,
> the user do not get any error message during creation of such archive.
>
> Tested on tar 1.26 (Fedora 20), confirmed on 1.28 compiled from sources.

This is a well known problem in gtar. Gtar did never handle multi volume 
archives decently. The way gtar tries to verify the correctness of a follow up 
volume cannot work. This is why star does not support to emulate to write the 
gtar multi volume method. Star should however be able to extract the archive
as star ignores the gtar verification method.

See: http://cdrtools.sourceforge.net/private/man/star/
and http://cdrtools.sourceforge.net/private/man/star/star.4.html for a 
documentation of the archive file format used by star. Star uses a method that 
is able to correctly verify whether you used the right folow up volume.

See also: https://sourceforge.net/projects/s-tar/?source=directory
and https://sourceforge.net/projects/schilytools/?source=directory for frequent 
source snapshots.

Jörg

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