Dumping to an exabyte tape drive

[Kevin L. Gross]

In article <776PKVH at dri.com> braun at dri.com (Kral) writes:
>In article <439 at cfa.HARVARD.EDU> wyatt at cfa.HARVARD.EDU (Bill Wyatt,OIR) writes:
>>
>>I think you'd better concede the last 10% or so, as long as dump can't deal
>>with EOT. And even if it could, I once had a nasty surprise when restore
>>broke because a multi-volume dump (9-track in this case) did't start at the
>>beginning of the tape. 
>>
>
>So the $64k question now is: why can't dump properly deal with end of tape?
>It's not like it's a new technology or something.

The way I heard it is that the EOF gap (filemark) used by dump is a physical
length of tape. On a nine-track, that length of tape for the EOF (and, I
suppose the EOT) is small relative to the amount of data one could place
there, if one wasn't using it for a filemarker. That same physical length
of tape on an 8mm tape takes up 10MB or more of possible data storage
because of the extreme cramification (technical term meaning TIGHT! ;-)

Although other data, specifically that from Eakins Assoc., makers of
the SPERAD (Scsi to PERtec Adapter board) interface, say that the
filemarkers are the equivilent of 2.2 MB, however, the dump program may
be using a much larger file mark than the filemark SPERAD considers normal.
(So sayeth Sequent anyway)

Possibly that is what is fixed in Sequent's version of an 8mm compatible
dump program called hdump, that costs an arm and a leg to purchase,
which is why I'm still using dump.

Hence, when you dump to 8mm tape the way I do, with about 17 filesystems,
you only get about 1.8 GB per tape instead of the advertised 2.3 GB. I'm
not exactly sure of the amount I lose per filemarker, but I do know if I
try to put more than 1.8 GB on the tape, I get a hung tapedrive because
it ran out of tape.

(BTW, anyone know how I get it to request a second tape without running
dump at the console? I run it via crontab script in the early AM.)

Right now, I am backing up about 1.68 GB + 170 MB (filemarks) = 1.85 GB.
(Uh, oh, I think I better archive some stuff. ;-)

If I try to backup more data/filesystems, say 20, I probably need to
subtract about 10MB per filesystem and another 10 MB for grins, from
2300 MB, leaving me with the number of MB I can safely backup, 2090 MB.
Take this with a grain of salt, my figures are probably off.  Actually,
I have been using 1.8 GB as the max, which was suggested to me by
various PWSK (People Who Should Know).

BTW, I use: /etc/dump ${LEVEL}udbsf 6250 32 9200 /dev/rmt12 on my
Sequent system for local and remote dumps where ${LEVEL} = 0-9.
-- 
-Kevin L. Gross          Systems Mgr.           klg at Summation.WA.COM
 As long as the systems are up, my employers don't care what I think

"Obviously, I am dealing with inferior mentalities."   -  Daffy Duck