According to Luke Mewburn:
>
>> I looked at the dump/restore command and started a dump of /home that was
>> about 50 MB.  dump then asked for another tape.  The DAT tape is supposed
>> to hold 2 to 4 GB with compression so I must be doing something wrong. :-)
>

Depending on the data you are backing up you may not get much over
2GB, about 150% (ie about 3G for you...) is average on our systems at
work using exabytes. 

>They're as good as any other. dump is the fastest way, but is highly specific
>to the filesystem format (and possibly even endianess).

And a reliance on a quiet file system for a good backup since dump
writes a table of all the file inodes first and then goes looking for
the data.

> gnu tar (the tar
>under NetBSD) is also reasonable.
>

I believe that gnu tar does not have this problem but to other tars
you must be very careful if you backup your system using it.  Most
tars that come with systems do not backup the /dev special files
directly - the slightly cleverer ones ignore /dev entries but I did
use an ancient sysv r2 machine on which the tar tried to _read_ the
files in /dev .... duh!!!  The upshot is that you may be sadly
disappointed if you expect to restore the entire system from a tar
tape - something that you can do with dump i.e. take a totally
screwed disk, newfs it and restore the partitions, run disklabel to
put back the boot block and you will be away.  With tar you would need
a partial system install.  I repeat, I am pretty sure that gnu tar
handles things properly but you need to be mindful if you develop the
habit that using tar elsewhere may not do what you expected.  Another
thing, dump seems to handle very long file names and "holey" files
better than tar (even gnu tar in my experience but I have an old
version).

Oh yeah, one final thing before I shutup - don't use absolute paths in
tar archives.  Again, I know that gnu tar handles this gracefully but
you may not always have it.

-- 
Brett Lymn, Computer Systems Administrator, AWA Defence Industries
===============================================================================
"It's fifteen hundred miles to Ankh-Morpork" he said.  "We've got
three hundred and sixty three elephants, fifty carts of forage, the
monsoon's about to break and we're wearing ... we're wearing ... sort
of things, like glass, only dark... dark glass things on our eyes..."
        - Terry Pratchett "Moving Pictures".