Re: Forced cooling requirements of HP DAT drives?

On Aug 18, 12:50 am, SpamTrapSeeSig <no-...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
I'd be interested to know where those figures come from.HP'sspec
quotes 12MB/s (uncompressed) for the current generation.

Own tests on various machines 6.2-6.7MB/sec using MSFT Backup.
DAT72 tape on DAT72 USB2 external.

I have a white paper on my other screen quoting DDS4 and DAT72 MTBF at
one million hours @ 12% duty cycle (based on testing and returns data).
Now I appreciate that's (a) out of date, and (b) not including the
reduction in MTBF caused by any external enclosure, but it amounts to
120,000 hours running time, and 40x the number you suggest.

HP DDS Drives Technical Reference Manual.
Volume 1: Hardware Integration.
Part Number: C7438-90901 Volume 1.

p40 - "Prolonging Head Life"
"...typical head life in excess of 6000 hours".
"This figure assumes that you use the appropriate tape for
the drive (such as DDS-4 media with DDS-4 drives) and that
you follow a typical usage pattern."
"You may not attain the typical head life when:
- You use an older tape format, such as DDS-2 tapes with a DDS-3
drive.
- A large proportion of cartridges loaded are being used for the first
time."

Seems pretty clear to me. Covers to DAT72.
For helical scan I go with the HP Head Life Hours figure.
Obviously Head Life is *Head Running Hours* - not drive Power On
Hours.
MTBF is a useful data point, but head life wins for me.


LTO head life is 30,000hrs.

And your data comes from... ?

IBM LTO-2.
Other LTO drives are double that (eg, Dell, HP) and later editions
have better head cleaning systems.


As with all tape technologies, LTO
and DAT both need to be fed at streaming rates for reliability. The 12%
quoted above IS rapidly diminished by 'scrubbing' (writing at
lower-than-streaming data rates), and it's one reason for the chunky
buffers the drives have.

My first encounter with DAT was HP C1533A in 1994.
I recall HP was the most reliable of all the makes available.
I also recall many installations failed to stream correctly and
thus both heads and tapes were subject to incorrect usage.

People also dropped the cartridges without regard, without
doing a retension even. The 4mm housings are not strong.

Not see DAT 8mm (160/320), there was always a racket
that the old 8mm tape was superior. Well yes, but it soon
died a quick death compared to DLT & LTO but they have
a long evolution from IBM DEC 3480 era - and big $$ spent.


DAT160 & DAT320 are very unreliable and nearly uneconomic to repair
compared to DAT72 from three repair shops.

Define "very unreliable" and state your source. I know one popular tape
technology from the 1990s that had an AFR (annualised failure rate) of
around 300%. It wasn'tDAT(and it wasn'tHP'seither).

Ever remember Colarado Jumbo or Travan... /dev/null?

By very unreliable I mean significantly higher failure rate when
subjected
to full capacity daily backups compared to DAT72. The evolutionary
fixes
from DDS1 to DDS5 improved reliability.

The source was 1 USA tape repairer and 2 UK tape repairers one
of which I know well. I still believe people are miss-handling tapes.

It is quite possible people are using the wrong tool for the job,
thrashing
DAT160/320 when something like LTO would be more suitable. I suspect
these could be Dell badged units bundled with servers and someone on
the purchasing side sees a budget saving over LTO.

LTO wins hands down, it has a long evolution path, it has WORM &
Encyrption capability - but it is expensive for small business.


The biggest downside with DAT used to be interchangeability.
The tolerance on drives was such that two drives could be at opposite
ends of the spectrum and thus write tapes they could read but others
could not. That I suspect was a batch of non-HP drives, although a few
HP drives suffered it - statistical tail end of the distribution as it
were.


Incidentally, the whitepaper I quoted isHPdocument 5982-8021EN from
2004. I'm sure later data is available, but I haven't time to go look.

As above.
.

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