[KLUG Members] a question concerning tar version 1.13.19

[Bryan-TheBS-Smith]

Rick Hayner wrote:
> the command for backing up my system is:
> from /, tar zclpf /dev/st0 .

Hey Rick --

I know tar is a big favorite among a number of people, but when it comes
to tape (or any other permanent backup medium), I like to shy away from
using compression with tar (vi either Z/Compression, z/GNUZip or
I/j/BZip2).  Normally, tar has excellent recovery capabilities in the
case of corruption.  Usually on those files in the tarball where the
actual corruption occurs are affected, and the rest of the archive can
be read.

When you compress a tar archive, you compress the archive _after_ the
tar operation.  As such, if the archive experienced corruption, the
uncompression step could render the file useless to the archiver.

For tape drives with hardware compression, this is not as much of an
issue (I just use tar without compression).  But for tape drives without
hardware compression, I like to use an alternative program.

   afio

Afio is cpio with per-file compression.  Instead of compressing the
entire archive, like in the case of tar with a compression switch, afio
compresses the individual files in the archive.  That way, if a
corruption occurs, it only takes out those files where it occured --
being that cpio also has excellent recovery capabilities like tar. 
Again, the archive itself is not compressed, only the files in it, so
that compression algorthim is _after_ the archiver, instead of before.

Since afio is cpio-based, any system that can read cpio can read afio
archives.  The only difference is that if you restore the files with
cpio, they are now compressed (and require an additional decompression
step).  But afio is available/buildable on just about any platform
anyway, so its just as easy to use.

-- TheBS

-- 
Bryan "TheBS" Smith    mailto:b.j.smith@ieee.org    chat:thebs413
Engineer  Absolute Value Systems, Inc.  http://www.linux-wlan.org
President     SmithConcepts, Inc.    http://www.SmithConcepts.com