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From: mark@hpcpbla.HP.COM (Mark Simms)
Newsgroups: comp.periphs.scsi
Subject: Re: High Capacity Tapes: Exabyte or DAT?
Message-ID: <9850023@hpcpbla.HP.COM>
Date: 24 May 91 10:08:22 GMT
References: <29543@hydra.gatech.EDU>
Organization: HP Computer Peripherals Bristol, UK
Lines: 68

Unfortunately, the DAT/8mm discussion is a bit of a religious one with
very little rationality and even less data.  I work for Hewlett-Packard.
I am involved in the development of HP's 3.5" form factor DAT drives.
Therefore I am biased.

If you find your Exabyte reliable and has suitable performance, then
you should probably stick to it.  Changing to DAT would involve a
whole new integration cycle before you could get the system working as
you like it.  It may require new drivers, new software and so on to
support DAT drives.  You may need to attach the DAT drives to a
different system in order to get them to work.

Having said that, how do the technologies compare?

The 8mm format has a higher capacity per tape and a higher transfer
rate.  The new 5Gbyte drives are impressive on paper, but I have seen
very little of them in practice.  8mm is a single vendor technology.
8mm has 5.25" full height form factor that cannot be easily shrunk.  8mm
is not supported by any major computer manufacturers as a long term
standard for data interchange.

The DAT format has a lower capacity than the 8mm format although the use
of 90m tapes and on drive data compression will help remedy this in
future.  DAT is shipped by at least three different vendors using
different mechanism suppliers.  HP and archive have 3.5" drives in
evaluation quantities now.  HP and DEC already support the DAT DDS
format and have a long term commitment to it.

HP and Archive have announced drives that support 90m tapes that bring
the capacity close to that of the standard 8mm model.  HP has also
announced a drive with on drive data compression which may improve the
capacity more.  I cannot recall whether Archive have announced a DC
product or not.  I would expect to see these drives available some time
this summer.

The current HP DAT drive is probably more reliable than the Archive
drive.  It can get more data onto the tape due to requiring fewer data
rewrites.  It is full height 5.25" form factor while the archive drive
is half height.  The HP drive is a bit of a bus hog.  (This is fixed in
the new HP drive that is comparable to the new Archive drive.)

The main reasons for switching to DAT are for long term support and data
interchange.  You may get gains in reliability.  If you have, or are
looking into getting, some systems that require half height or 3.5"
drives, then you should consider DAT.

Probably the most important factor when choosing a backup system is the
amount of support you get from the vendor.  If a system vendor has a
standard backup system, then use it.  It will probably be the most
reliable.  If not, then find someone who will sell you a complete
solution including support.  It may cost a little more, but you are more
likely to get a system that works.

Mark Simms

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Opinions expressed are my own and are not intended to be an official
statement by Hewlett-Packard Company
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Name:         Mark Simms
Profession:   Software Engineer
Occupation:   Research and Development
Organization: Hewlett-Packard Computer Peripherals Division
Unix-mail:    mark%hpcpbla@hplb.hpl.hp.com
Address:      Filton Road, Bristol BS12 6QZ, United Kingdom
Phone:        +44-272-799910x22174
Fax:          +44-272-236091
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