Re: Tape Backup And Block Size

[glhenni@cs.sandia.gov (Gary L. Hennigan)]

"Chris Hoover" <wax_man@bellsouth.net> writes: 

First, it'd help if you wrapped the lines in your posts. Those long
lines make it look like crap in a lot of newsreaders.

| Does anyone know how to find out what the proper block size is for a
| tape drive?  I have an Exabyte 8200 scsi tape drive (8mm 2.5 gig),
| that I bought used with no documentation.  I've looked at the exabyte
| home page, but did not see any mention of block size. 
|
| I've tried to backup with dump, but it is not getting the right
| block size.  This is causing it to tell me I need multiple tapes when
| everything should fit on one. 
| 

It's not an issue of block size, you just need to tell dump what the
size of your tape is. I don't recall the specifics of the Debian dump
command. Some versions of dump simply support specifying how many
kbytes will fit on the tape with the "C" option. On others you have to
figure out the correct length (s) and density (d) specifier. So if
you have an 8200 I believe the tape capacity is 2.2GB? Here's a
snippet out of the IRIX man page for dump that you might find useful:

</Begin quote of IRIX dump man page>

     If	you do not wish	to use the C option, then when using drives with no
     interrecord gaps (that is,	almost every type except 9 track), use the c
     option and	the formula

	  capacity in bytes = 7	* densityvalue * lengthvalue

     and round down a bit to be	conservative (allowing for block rewrites and
     so	on).  The density should be kept under 100000 to avoid overflows in
     the capacity calculations.	 Thus, for a DAT drive with a 90-meter tape (2
     * 10^9 capacity), one might use:

	  2000000000 = 7 * 47619 * 6000

     or, rounding down

	  dump 0csd 6000 47000

</End quote of IRIX dump man page>

That part about the "c" option may not be relevant to Debian. On IRIX
the "c" option is used to indicate a cartridge type device (e.g., QIC, 
8mm, 4mm, etc.). Other arguments may also differ between Debian and
IRIX so you'll want to read the man page for dump on Debian to see how 
that corresponds to the above.

| I've been working on this for a while, and haven't gotten it right
| yet.  And to make matters worse, I lost my 5.1 gig maxtor about 2
| weeks ago w/o a good backup.  So I really want to get this figured out
| to prevent any more catastrophic data loss. 

It's rather confusing. Personally, I'd recommend tar. It doesn't have
this problem, it just keeps writing to the device until it gets an EOF
from that device, and it has the advantage of being portable to other
systems running GNU Tar and it's able to backup any type of file
system, including DOS FAT, something dump can't do.

The other option, with which I'm not that familiar, is cpio. It's also 
gotten high marks as a backup utility among Linux users.

Good Luck,
Gary