From: dusan@cs.uq.oz.au (VK4FCW)
Newsgroups: comp.periphs.scsi
Subject: Comparative study on tape drives
Date: 14 Oct 92 02:03:28 GMT
Reply-To: dusan@cs.uq.oz.au (VK4FCW)
Followup-To: uqcs.followup
Organization: Computer Science Department, The University of Queensland, Brisbane, Australia


1. Background

We have been using Exabyte EXB-8200 tape drives for backups in the
Department of Computer Science for about two years now. During that 
period we had to replace the drive two times (hardware failures). 
Since the last replacement (a year and a half ago) we have not 
experienced major problems with the drives.

The Exabyte tape drives are used for unattended backups at night during
weekdays. Since we run backup checks as well, duty cycle is about 23%
(drives in use for about 8 hours every day).

New workstations are about to arrive in our Department and there is a need 
for even higher-capacity tape media. There are four (at least that many I 
can see) logical paths to follow:

  - DAT 8 GB tape drive.

  - Exabyte 5 GB tape drive.

  - QIC tape drives (have potential to
    host 30+ GB in several years from now).

  - DD-2 tape drives. Ampex has
    developed this new high-density
    helical scan tape format. It is
    based on D-2 19mm cassettes (like
    ones used in broadcast TV industry).
    It offers 15 MB/sec transfer rate.
    Supported cassettes go up to 150 GB.

The latter two have probably not been tested by many users (or are 
not even available yet), so I am not keen on predicting which one
might win in a long term run.



2. Your help

The network has always been very helpful in giving good, resourceful, and
reasonably objective answers to users' enquiries.

I have searched some older files and archived newsgroups at our site 
(looking for comments on DAT and Exabyte tape drives). Some of them were 
old and not usable at all.

I have taken the trouble of writing this message in hope that we can 
enter a constructive discussion on the future of tape drives and backup
media.

You can mail your comments and tell me about your experience using
any of the above tape drives, or you can post it directly to the newsgroup.
I would like to know about your past experience, as well as your 
ideas which technology will "win" in the near future. We all are fully
aware that best solutions do not necessarily conquer the market. Demand
for a certain product depends on many factors.

In ay case, I shall post a summary on this topic in about three weeks from
now (if there is anything to summarize at that time).



3. Basic information

I have gathered some data (available through various data-sheets and 
documentation). It is not a full list of features, so accept it as an 
entry point for comments.

I have taken two models into account although I would be more than
happy to hear about other products (like the new Archive Turbo-Dat drive).

Characteristics                           Tape drive type
----------------------------------------------------------------------------
                               EXB-8500S                   HP 35480A

Capacity
--------
User-selectable cartridges     300 MB to 5,000 MB          Up to 8,000 MB
	                                                   (90 meter tape)
                                                          Using Data Compression
							   Lempel-Ziv in
							   real time

Tape length
-----------
Supported (unit is meter)      60, 90, 112                 60, 90
                               (maybe others?)

Performance
-----------
Transfer rate    asynchronous  1.5 MB/sec                  1.5 MB/sec
		 synchronous   4.0 MB/sec                  5.0 MB/sec
                 sustained     500 KB/sec                  732 KB/sec

Buffer size                    1 MB                              

Effective tape-to-head speed   3810 mm/sec 

Search speed                   Max. 37.5 MB/sec            30 sec for any part 
							   of a 90 meter tape

Form factor                    5 1/4 inch                  3 1/2 inch
                               (Industry standard)         (Compact) 

Track density       8500 mode: 64 tracks/mm (1638 per inch)
		    8200 mode: 32 tracks/mm (819 per inch)

Areal density       8500 mode: 0.114 million bits/sq mm 
			       (74 million bits/sq. inch)
		    8200 mode: 0.054 million bits/sq mm
			       (35 million bits/sq. inch)

Power consumption
-----------------
Typical                        15 watts                    5 watts

Reliability
-----------
Non-recoverable error rate 
in data interchange mode       10exp13                     N/A

MTBF                           40,000 hours                50,000 hours

MTTR                           <30 minutes                 N/A

Physical dimensions
-------------------
Height                         82.5 mm                     41.3 mm
Width                          146 mm                      101.6 mm
Depth                          203.2 mm                    150 mm (excluding
								  front panel)
                               (Model 8505
			       is about half the 
			       size of 8500)

Price (valid during Oct 92)
---------------------------
Not including sales tax        4,808 AUD                   3,200 AUD



Thank you in advance for any comments.

Dusan