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10 RAIT (Redundant Arrays of Inexpensive Tape)


This article is from the storage FAQ part1, by Rodney D. Van Meter with numerous contributions by others.

10 RAIT (Redundant Arrays of Inexpensive Tape)

There are several tape array products on the market:

Data General is selling the CLARiiON Tape Array Subsystem comprising
between five and seven 4mm DAT tape drives. Data can be recorded in
RAID-like striping redundancy, mirrored, or in conventional DAT layout.
This unit can provide up to 30GB of unattended contiguous storage. The
tape drives can record at sustained rates of 183 - 732 KB/second each but
customers should expect sustained backup at around 1 megabyte/second of
compressed data after accounting for host overheads. Data General is
working on a seven tape caddie to hold tape sets together. It is essential
that tapes in a RAID group not be separated.

NCR announced a tape array software product for NCR uniprocessors and
System 3450, System 3550 and StarServer Systems running UNIX V R4.2.01.
This tape array software yields faster and more reliable backup of large
database and file servers than with any single tape drive available today
but uses customers existing tape devices. It writes simultaneously to
multiple drives and can use array techniques to recover from loss or
failure in any single tape.

The motivations for tape arrays seems to parallel those for disk arrays:
        -       higher bandwidths
        -       increased reliability

(dwilmot@crl.com, Dick Wilmot, Editor, Independent RAID Report)

Pick up any DEC related trade rags and you can find an ad for an 8mm tape
array.  The ad I just found is by Contemporary Cybernetics and uses two
five GB 8mm drives with compression - they CLAIM to be able to get 50 GB os
storage total - but how many customers have 50 GB worth of 5:1 compressible

Anyway - the ad doesn't mention RAID, but they support RAIDish (!) features
such as striping and mirroring.  It also supports offline tape-to-tape
copy and will automatically cascade onto the second tape when the first
one fills (useful for utilities that can't deal with multi-drive/multi-

I SEEM to remember someone having something like this with more drives, but
of course I couldn't locate the ad.

I would be really interested in seeing something like this for 3480 since the
transfer rate is already quite high...

(tbodoh@resdgs1.er.usgs.gov, Tom Bodoh)

At the Monterey IEEE Mass Storage Conference in April '93, Ann Drapeau
from Randy Katz's group presented a paper on striped tape.

The National Storage Lab High Performance Storage System reportedly
supports striping of removable media in the system software.


Something that came through the newsgroup recently (95/2/5):

Tape Arrays
High Performance tape drive units for large networks and minis.
Fast: up to 4Megabyes/second
High Capacity: from 24Gb on 4mm DATS to 60GB on DLTs; with 
autoloaders,up to 616GB
Flexibility: Stripe data across 4 drives, mirror data, 
stripe 2/mirror 2 - double your speed while creating an off-site
storage copy; off-line copy; pass-thru mode, etc.  
Transparent to your backup software - no changes or retraining
Compatible with all major OSs; including Novell, WindowsNT,
Unix, Sun, HP, Silicon Graphics, VMS, etc.
For More information:
William Wirth

Just spotted this in a PC rag. Andataco can stripe, mirror or RAID
DLT, 8mm or 4mm. Check out http://www.andataco.com or call
800-334-9191 or +1-619-453-9191. Or email inquire@andataco.com. 
(Andataco is an integrator for numerous storage products including
RAID arrays.)

Compaq now has a DLT tape array. Some specs available at
http://www.compaq.com. Stripes or does RAID 5. (rdv, 96/4/17)

Tecmar makes a tape array with up to 30 (custom) drives. A "rotating" spare is
used to gradually back up the entire system. (Georg Feil,
http://www.sgl.ists.ca/~georg, georg@sgl.ists.ca, 96/10/17)


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