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From: mab@aplcen.apl.jhu.edu (N Brockway mark alle 301-725-8427)
Newsgroups: comp.sys.sequent,comp.periphs
Subject: 8mm cartridges or 4mm DATs for backups?
Message-ID: <1991Mar25.193731.5700@aplcen.apl.jhu.edu>
Date: 25 Mar 91 19:37:31 GMT
Distribution: na
Organization: Johns Hopkins University
Lines: 43

We currently have a dilemma in operating our machine.  We have almost 2GB
of disk data that needs to be backed up and it takes way too long :-(.  This is
the hardware/software configuration:

	Unisys U6000/80 (Sequent Symmetry S81)
	Dynix 3.0.12.1
	SCSI Bus with 12 1GB SMD Disk Drives
	3 Dual Disk Controllers
	Multibus with 2 1/2 QUAD Tape drives
	128 tty ports (connected to the Multibus)
	Mapper DBMS

We use the Mapper software to do our incremental and full backups.  This is a
software-specific PURGE procedure.  To do the full backup takes over ten hours.
What we would like to do is purchase either a third-party 8mm cartridge device
or a Unisys 4mm DAT device.  The third-party 8mm drives I've looked into run
off the Multibus using a PERTEC interface.  Unisys does not currently market a
8mm device for this machine with this (or any later version) operating system.
Their 4mm DAT drive runs off the SCSI bus.  I have the following questions:

	1) I do not know much of anything about these two options.  Can anyone
tell me what are the advantages/disadvantages of these two technologies?

	2) Unisys Customer Engineers claim that given that their 4mm runs on 
the SCSI and that the 8mm will run off the Multibus, the 4mm throughput would be
better.  Can any shed some light on this?  [I hate to rely on someone who is
looking to make money off my decision.]

	3) Could anyone give me an idea of how our backup times would be
reduced with these options?

	4) What other considerations are there in using these technologies
(i.e. compatibility, future viability, etc.)?

	5) Do we need to upgrade the operating system to ptx in order for the
new peripherals to work?  Unisys wants to force us to ptx for their 4mm DATs.

Please excuse my ignorance.  Any information is greatly appreciated.
-- 
Mark A. Brockway               | Internet mab@aplcen.apl.jhu.edu
Bell Atlantic                  | Phone    (301)595-2357
11700 Beltsville Dr., Ste 600  |
Beltsville, MD 20705           | ** These are my own opinions **