Re: [SLUG] Re: large files on DVD -- single byte error = _toasted_ DVD set

From: Eben King (eben1@tampabay.rr.com)
Date: Thu Dec 02 2004 - 12:38:11 EST


On Thu, 2 Dec 2004, Bryan J. Smith wrote:

> On Thu, 2004-12-02 at 03:28, Eben King wrote:
> > So I back up the installation of that Other OS by basically creating a
> > partition image and compressing it with bzip2 (note: bzip2's output is
> > less than 2% smaller than gzip's, but it takes MUCH longer to create).
>
> Consider lzop if you're worried about speed, comparison of how much you
> can fit on a CD and how long it takes:
> http://www.samag.com/documents/sam0204c/sam0204c_s1.htm

Sounds promising; I'll try it. Found http://www.lzop.org/ .

> > A 13 GB partition compressed to 8G. I split into two chunks, each slightly
> > smaller than a DVD.
>
> Okay, now you're making your "backup" almost totally _inrecoverable_.
> If you have even a _single_ byte error on _either_ DVD, then you
> basically toast your copy. Not good.

It would be vulnerable to damage (on one level or another) no matter what
simplistic method I used to divide it. That archive contains one 13GB
file, an image of an NTFS filesystem; the System Rescue CD uses kernel
2.4, which can't write to NTFS filesystems, so I can't do a file-level
backup. Not that I trust XP to store all its needed information in
Linux-readable files anyhow...

Is there any way to store enough of a parity check to recover from errors?

> Consider:
> http://freshmeat.net/projects/afio/
>
> afio is USTAR (cpio = 5KB blocks, tar = 10KB blocks) compatible,
> per-file compression inside archive, inherent "split" functionality,
> etc...
>
> You could use afio to make individual archives that are 500MB or so,
> then make an .iso of that for DVD to make as many DVDs as you need. And
> you are _only_ backing up the files you need.

Won't help; see above.

-- 
The powers in charge keep us in a continuous stampede of patriotic fervor
with the cry of national emergency. Always there has been some terrible evil to
gobble us up if we did not furnish the exorbitant sums demanded. Yet, in retro-
spect, these disasters seem never to have been quite real. -- Gen. D. MacArthur

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