using tar with DAT drives

Ian Pallfreeman ip at
Thu May 31 14:51:41 BST 2001

> I have a machine running 4.0 to which I have fitted a 12/24 DAT drive.
> Using tar, the drive is recognized and seems to work perfectly but
> I have recently found that despite only having around 3Gb of data on
> the system and trying to backup to a 12Gb tape - only some of the 
> data is actually being archived.

Meaning what, exactly? Are you getting "end of tape detected"? Some other
error? Forgetting to back up all your partitions?

> I have read the man page a number of times and been told that I can
> change block sizes or block counts but I don't actually know what
> the parameters should be. 

It varies from drive to drive. Most DATs can handle 64K blocks, so you'll
want something like:

	tar cbf 128 /dev/nrsa0 /data/to/backup


	dump a0bf 128 /dev/nrsa0 /partition/to/dump

Bigger block sizes means more of the tape is written with real data, rather 
than being used for inter-block gaps, and the drive will generally eat data 
faster. The downside is that if you get an error on the tape, you'll lose 
more data, but that usually isn't an issue. Also, I can't really see you 
losing 9GB of tape even using small records, so it may be another problem.


More information about the Ukfreebsd mailing list