[comp.unix.ultrix] Request information about DEC SCSI-DAT drives, partitioning SCSI

aem@aber-cs.UUCP (Alec D.E. Muffett) (11/15/90)

Hi there! 8) At our site we've recently been through a great deal of
hassle trying to purchase some mass storage media for a backup system.

We've developed the technique of taking incrementals by dumping the user
partitions of our large mainframe servers (2x DEC 5830s) over NFS to the
local disk of of a smaller machine which has tape drives (Gould NP1).
We've modified 'dump' to remove a file-locking bug on /etc/dumpdates,
and we run 3 or 4 dumps-to-the-tape-servers-local-disk in parallel, when
the userload is low.

We then use dump (again) to put the tape-server's storage partition onto
tape.  This bit is very quick, since our Gould's drives stream a 6250
tape like the blazes, and it's basically copying 1 only file.  It all
works very nicely.  8)

However, the powers that be have decreed that the Gould must go, and it
is to be replaced with our brand-spanking-new DECStation 5000/200, with
about 2Gb filestore.  This seems to be up to the job, barring one little
problem.  It hasn't got any tape drives yet. 

DEC then leapt in with impressive statistics about a new SCSI-DAT drive,
using DDS format, storing about 1.2Gb per tape, that they could sell us.

The wonderful thing about these tapes is that they may be partitioned up
with an index block at the start of the tape so that a high-speed seek
may be performed to get to the start of one of these 'partitions' and
then the tape can be read from that point.  This sounded wonderful for
storing 3x330Mb dumps per tape and would fit in with our current
strategy.

We've bought one - nothing to do with me, I might add...

What I'd like to know as a programmer is:-
	- Who makes these drives
	- Do they really work
	- How do you access this 'multi-partitioning' facility ?

We have no documentation at all for this thing, it hasn't arrived yet,
and requests sent to DEC for documentation have been unanswered.  This
multi-partitioning/seeking sounded like it was done in hardware on the
drive but it doesn't fit in with the description of anything you can do
with SCSI tapes using the tz(4) SCSI tape interface. 

Are we gonna have to have new tz drivers before they will work, or is it
a cheat with a library ? Is it possible to use this facility with DEC
hardware ? Basically, is there anyone out there we can talk to about them ?

		For all information you can give,
				Many thanx in advance,

					alec
--
JANET	aem@uk.ac.aber or uk.ac.aber.cs
INET:	aem@cs.aber.ac.uk or aem@aber.ac.uk
UUCP:	...!mcsun!ukc!aber-cs!aem
ARPA:	aem%uk.ac.aber.cs@nsfnet-relay.ac.uk|aem%uk.ac.aber@nsfnet-relay.ac.uk
BITNET:	<play around with aem%aber@ukacrl, ok ?>
SNAIL:	Alec Muffett, Computer Unit, Llandinam Building,
	UCW Campus, Aberystwyth, UK, SY23 3DB