Path: utzoo!attcan!uunet!munnari.oz.au!metro!usage.csd.unsw.oz.au!decus!churchill
From: churchill@decus.com.au (Jack Churchill)
Newsgroups: comp.sys.dec
Subject: Re: Exabyte (8mm) versus DAT (4mm)
Message-ID: <3201.269c66a7@decus.com.au>
Date: 12 Jul 90 02:01:43 GMT
References: <9007061713.AA01816@stc06.CTD.ORNL.GOV> <1881@proa.SV.DG.COM> <13113@cbmvax.commodore.com> <1990Jul9.230745.26256@hayes.fai.alaska.edu>
Organization: DECUS, South Pacific Chapter
Lines: 35

> There was a long article in one of the design rags a couple of months ago about
> 4mm vs. 8mm, from the standpoint of coding methods.  It claimed that 4mm uses
> the same error correction methods designed for human-listener audio playback,
> while 8mm uses algorithms specially tuned for computer data storage.  The
> conclusion was that the 8mm algorithms were far superior for archival
> applications.  Since this article was written by an Exabyte engineer, we can
> be sure it is unbiased and accurate, right?
> 
> But the point of the original posting, I think, is whether 8mm or 4mm is the
> better overall choice for backups.  I'm very interested in this question
> because I'll be buying one or the other shortly and haven't really decided
> which.  I've seen others post similar queries but I haven't seen an
> enlightening followup or summary.
> 
> The 4mm seems to cost substantially more (~1.5x) that the 8mm for initial
> hardware.  Currently, 4mm stores half as much as 8mm per tape.  This would
> seem to make 8mm the best buy.  However I've seen enough questions about
> 8mm reliability to make me wonder.  How much downtime do 8mm users see?
> Are problems due to the exabyte mechanism itself, or the supporting hardware
> or software?  Has anyone been using 4mm long enough to make a meaningful
> statement about its reliability or overall impressions?  If this has been
> addressed in print somewhere, references would be appreciated.
> 

I think the time is well overdue for a proper and unbiased evaluation of
all backup mediums.  This includes optical disks as well as 4 & 8mm.  We
have been using 8mm for about 8 months with no problems.  The only complaints
are the search and transfer speeds during restores when people (not me)
are in a hurry to read a file.

Jack N. Churchill                            | E-mail:
CSIRO  Division of Exploration Geoscience    | churchill@decus.com.au
Remote Sensing Group                         | Phone:  +61 2 887 8884
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