Is there a backup utility to backup to LTO tape that's not TAR, PAX, or CPIO?

Question

I'm using Solaris 11.3 and wish to occasionally backup a bunch of large VM's and disk images directly to a used LTO6 tape drive bought off Ebay but even though Solaris TAR has the "E" flag to allow files > 8GB in size this is of no use to me because either way I understand that TAR simply aborts if it hits a media error when reading from a tape so I do not want to use it. CPIO will continue as apparently so will PAX but those two can't cope with files over 8GB and are deprecated and so will never do so.

Is there any successor to CPIO that can do everything CPIO does but will also backup files > 8GB? or a TAR replacement that will still continue? I'm not interested in portability so don't care what archive format is used as long as I can restore and do the usual stuff that proper archivers do like preserving timestamps, etc. etc.

I'll probably have to install Amanda or Bacula to get this job done and since I'm relatively new to *nix and finding no readily available command line program to do this in any other unix or Linux variant is a surprise as reading on the net I see that people were complaining about this issue and previous 2GB limits shortly after the turn of the century.

Answer 1

You are right with your size assumptions on cpio, but please note that cpio is not a single format but rather four or even more completely incompatible formats with different constraints. This is why the cpio format has been declared outdated by the standard. For every enhancement to the cpio format you would need to create another incompatible format, so cpio is just not prepared for the future.

Given that the cpio formats are not blocked, it is extremely hard and error-prone to resync the reader after a read error. So cpio is not recommended for archival. Anyway, your claim about error recovery with cpio is not related to cpio itself but to the AT&T implementation, so beware of the GNU implementations....the feature you refer to is undocumented, similar to the fact that Sun/AT&T cpio may be used to replace binaries of running programs without causing problems. The latter is something you get with star -install as a documented feature.

TAR on the other side is a format that (thanks to the new enhanced tar format standardized in 2001 by POSIX based on a proposal from 1997 by Sun Microsystems) that can can be enhanced without future incompatibility problems.

If you have a read error on a tape, it is questionable whether the kernel driver will permit you to read past that problem anyway. But I just checked the Sun cpio and it seems that it internally translates EIO into some kind of EOF that did not return data. The main problem here is that it seems that Sun cpio does not remember such a problem in it's upper layers.

If you like to get something similar to what cpio does, I recommend to use something like:

sdd if=/dev/rmt/0 bs=126k -noerror try=0 | star -xp -i

Replace 126k with your tape's block size and use a proper if= parameter.

Some further notes:

gtar is able to do backups, but it frequently fails to restore it's own archives. This happens e.g. when you use the gtar incremental backups with non-trivial differences between two incrementals.

staron opencsw is not recent. I recommend to compile a recent version from the schilytools package at:

http://sf.net/projects/schilytools/files/

In general, schilytools are updated with typical frequency of once every fortnight.

The current man page for star is at:

http://schilytools.sourceforge.net/man/man1/star.1.html

See also

http://schilytools.sourceforge.net/