Re: [Bug-tar] [PATCH] p7zip support

[Doug McLaren]

On Mon, Jan 02, 2006 at 06:40:39PM +0100, Robert Millan wrote:

| > Sure, that's temporary space. But anyway, one must have twice as much
| > space available when restoring from a 7za archive than when restoring
| > from an archive compressed with another compression method. And that's
| > a big drawback.

It's also just plain ... nasty.

|   - It depends on what you do.  In my example (thousands of small files), you
|   get a significant gain in permanent space for a minimal cost in temporary
|   space.

Wouldn't `tar -zcvf' or `tar -jcvf' benefit similarly (but just using
gzip or bzip2 rather than p7zip?)
 
|   - It's only an implementation issue.  It can be fixed later by implementing
|   streaming properly.

Perhaps, but it just doesn't seem ready for tar use today.  Using
temporary files to simulate a stream is, as I said ... nasty.  It's
workable if somebody wants to back up a few hundred MB here and there,
but what if somebody wants to back up their entire filesystem to tape?
Unless your filesystem is < 50% used, it's not likely to work.

(Of course, to play devil's advocate, gzip isn't good for large tape
backups because one single error will make the rest of the gzip'd
stream unusable, and bzip2 isn't so good because it's so slow.  And of
course p7zip is even slower.)

In any event, the source for p7zip is here --

   
http://easynews.dl.sourceforge.net/sourceforge/p7zip/p7zip_4.30_src_all.tar.bz2 

in case anybody wants to look at it and maybe even fix it.

And as was discussed in the previous thread, you can use your p7zip
wrapper with tar today with no patches -- just use 

   tar --use-compress-program=p7zip ...

Ultimately, there's lots of compression programs out there, and gnu
tar will let you use any of them, as is, right now, as long as they
streams as input and output and support the -d flag.

-- 
Doug McLaren, address@hidden
`If one studies too zealously, one easily loses his pants.' -- Albert Einstein