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Date:      Mon, 30 Dec 1996 19:28:09 +0000
From:      Simon Reading <aat81@dial.pipex.com>
To:        grog@lemis.de (Greg Lehey)
Cc:        freebsd-hardware@freebsd.org
Subject:   Re: DAT reliability
Message-ID:  <3.0.32.19961230192648.0068db48@pop.dial.pipex.com>

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Greg,

Thanks for the mail.  Apologies if this reply is a little long.

At 14:48 30/12/96 +0100, Greg Lehey wrote:
>Simon Reading writes:
>> 1. As you say, the SDT-7000 is a new design. Like ANY new product, I would
>> expect more teething troubles than one which has been out in the market for
>> longer. (NB. I'm not saying this was the cause of my problems).
>
>I don't think that *any* is valid.  Many new products have teething
>troubles; many others don't.  During this discussion I have come to
>the conclusion that the HP C1533A is a whole lot more reliable than
>the 35480A, for example.
Maybe ANY was a rash generalization ;-)

>> 3. How many people listen to their DAT player four hours _every day_?  How
>> long would it last if they did?
>
>I listen to my CD player for hours every day.  It's about 7 years old
>now.  I don't have a DAT player, but I would guess that the typical
>duty cycle for hi fi equipment could be higher than for tape backup
>devices.
I've used personal cassette players (cheap, expensive, different brands)
for three hours a day, on average, they lasted about a year.  I have a
personal CD now, so this is no longer a problem.  I don't know about the
duty cycle of DAT or HIFI.

>>>   I would guess that the 5200 has been
>>>  out for longer and that any bugs/problems would be more likely to be
>>>  observed/sorted out than any with the 7000.  The small price difference
>>>  between the two models make me think that there has been little change in
>>>  the funamental mechanism design and that 8000rpm may be too fast to
>>>  transport the tape using the existing mechanism.
>>>
>>> The price of the unit has little or nothing to do with its cost,
>>> design or taste when deep-fried.  I've observed over the last few
>>> years that as a general rule, most DAT units "just work".  I've only
>>> met a few "persistent plaintifs" who seem never to be able to get a
>>> working unit.
>>
>> There are two separate issues here.
>> 1. Infant mortality.  The reason why I returned my SDT-7000 was because it
>> didn't work.  
>
>Agreed.  But there was evidence in your case that the device had
>already been installed somewhere and returned for some reason.
True.

>> The reason why I have not exchanged for another SDT-7000, is in case
>> it is a problem with the batch.  (I can't afford to waste time with
>> another dud).  Fait accompli.
>
>You're assuming that you would be better off with another brand.  I
>don't think that these problems extend to whole batches.
>> 2. Expected Lifetime. As stated before, I'm much more interested in how
>> long I could expect a DDS-2 to last.  From correspondence I've received I'd
>> guess 18 months+ light usage, six months or so heavy usage (I'm happy to be
>> corrected on this).
>
>I suspect you're (mis)quoting me here.  I was talking about the 35480A
>when I mentioned 6 months.  I'm pretty sure I've had the C1533 for
>well over a year, and it has had well beyond the expected 12% duty
>cycle in that time.
These were intended to be ball park figures rather than direct quotes.  In
the interests of accuracy, and for reference, I have quoted mails which
have been sent to me, below.

David Dawes writes:
>I've had a 35470A for about 3.5 years now, and haven't had any
>real problems.  I've had a few I/O errors recently, but nothing that
>a pass of a cleaning tape doesn't fix.

phr@netcom.com (Paul Rubin) writes:
>I have a C1533a now a little over 1 year old.  I've had no problems
>with it but my usage has been pretty light.  Any DAT drive will
>wear out after a year or so of heavy usage.  

Al Dykes <adykes@panix.com> writes:
>I run a shop that has 7 tape drives, 4 are HP-DAT and three are
>Exabyte 8mm. The exabyte systems backup about 4GB every night.  The
>DAT drives do about 3GB. I do 100% verifies on about half my backups.
>That of course doubles the # of hours on the drive. All of these
>systems are at least 2 years old. The oldest is just about 3 years
>old.
>Until this week all the DAT drives were HP35480A OEM units. In my
>experience DAT drives work for about 2 years of heavy use and die
>suddenly of something that is clearly mechanical, generally eating a
>tape in the process. I can live with this. 

Greg Lehey <grog@lemis.de> writes:
>>> Warning: Quality control on these drives varies greatly. . Neither
lasted more than
>>> 5 months.
>
>Well, this sounds very much like a report from me.  But two things
>don't fit:
> . .
>2.  I was talking about 37480As.  These are an older version of DDS-1
>    drive.  I do have a C1533A, and so far I've had no trouble with it
>    (more than 6 months, anyway :-) I think, in fact, I've had it
>    about 15 months, and I do a nightly backup which usually fills a
>    tape.

Rainer Vonsaleski <rainer.vonsaleski@edgebbs.com> writes:
>I bought an HP C1533A in November 1995, and I have been very happy
>with it.  Initially, there were some problems getting the termination
>right (My Micropolis 1G drive *looked* to be terminating the bus,
>but it wasn't).  None of the problems were the fault of the C1533A.
>
>The C1533A has a most unusually complete set of error statistic logs
>available.  The performance with 90-meter tapes (hey, I'm cheap)
>is fantastic.  I trust this thing!  This is from someone who wants
>a medium to transfer hundreds of reels of 9-track tapes to for
>archival purposes.
>
>I've spun about 50 full tapes in 13 months.  The C1533A has behaved
>flawlessly.  If I had the choice to make over today, I would choose it
>again, even though the Sony is 33% faster (on paper).  Why?  (1) Most of
>my surprises with HP over the years have been pleasant surprises.
>(2) Sony is playing catch-up, and their new drive is still much too
>new.
>
>If the Sony is giving your grief, I'd return it for the C1533A.
>In a second.

There were also been a few comp.periphs.scsi postings (which I have filed.
. on a server which has gone down :-( )

Greg writes: 
> Simon Reading writes:
>> Does one DDS-2 manufacturer produce more reliable drives than
>> another?  I don't think we're much closer to an answer on this
>> question.
>
>There are bound to be differences in reliability.  It's just the
>question whether they are statistically relevant.  
True.  This is necessarily a problem of considering anecdotal evidence.

> My feeling is that
>the technology has matured considerably in the last 5 years, and that
>it will continue to mature.  As a result, I would prefer a new model
>over an old model, even if other factors (capacity, speed) remain the
>same.
Is it not true that existing products continue to be tweaked as problems
are observed by users?

- For instance on my car, the car locks were replaced with a new design
following problems experienced in the cold.
- A certain make of car engine had a revised valve gear following
(unpublicized) user problems.
- TV designs for the same model are updated as better components become
available etc.

Regards

Simon





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