On Thu, 12 Apr 2001, Maarten van den Berg wrote:
For backup purposes, I need to save big dirs of data to tape. The easy way: a gzipped tarball (eg: tar zcvf ..). Another method: tar .. ; bzip2 ...-> you get a tar.bz2 which has better compression ratio.
BTW with any recent GNU tar you can use the "I" switch (instead of "z") to transparently use bzip2.
what does it happen when you have only a one big file (tarball, eg)????? Would you lose more data than the strictly affected by the tape failure? Would you lose all the data?
You'd lose all the data, that is why using a compressed tarball on tape is a bad thing. Either compress files individually or maybe rely on the builtin hardwarecompression of the tapedrive, if you like.
You wouldn't loose all the data. Both tar and bzip are just streaming so you'd be fine up to the damaged part. I'm not shure if you can recover behind the damage. There is a tar-repair tool somewhere... For a commercial tool I can recommend BRU (www.estinc.com) which is a nice enhanced tar replacement. They claim improved resistance to damaged data but luckily I haven't had to test this feature.
Personally I dropped using any compression, since the major part of what I backup are mostly compressed files anyway (gif / jpg / mpeg etc.)
That's true. We have a server full of JPG and TIFF files (160G) and there's no compression whatsoever. You only get half (or quarter) of the advertised "volume" on a tape :-(
I read that .bz2 is more "secure" (=robust) than .gz (maybe in tape howto).
I would be surprised if by robust you mean it's possible to reconstruct all data from a damaged file. Compression is all about removing redundancy in your data and reconstruction is about adding and distributing redundancy. If by robust you mean it's possible to recover partial data from a damaged file then it sounds possible but I don't know anything about the internals. Robert -- Robert Casties --------------------- http://philoscience.unibe.ch/~casties History & Philosophy of Science Tel: +41/31/631-8505 Room: 216 Institute for Exact Sciences Sidlerstrasse 5, CH-3012 Bern Uni Bern (PGP key on homepage: D7 2B DE 64 2D 65 16 A0)