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Forced cooling requirements of HP DAT drives?

 
 
js.b1
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      08-13-2011, 12:14 PM
Do HP DAT drives (72 160 320) require forced air cooling?

Their external enclosures do include a fan - but is that for the PSU,
or the DAT drive itself?

A DAT drive of that generation does have 3 vents at the front and a
dust-shuttered external door.
- The 3 vents are open albeit of limited gap and do direct air over
the PCB at the base of the drive.
- Older DAT drives used an internally opening door, permitting boulder
sized dust to be drawn in and bake on the heads, an external door is
pulled shut by negative air pressure.

I recall a major cause of DAT drive failures was a) dust ingress and
b) overheating.

FREECOM external DAT drives are a HP mechanism in their box - but just
vents at the rear and no fan cooling, so at best cooling by
convection. I am not sure if this is marketing or engineering!

Do HP specify forced air cooling for their mechanism?
 
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js.b1
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      08-13-2011, 12:43 PM
HP Hardware Integration... HP DDS Drives Technical Reference Manual...
covers DAT 72... HP Restricted... hmmm...

p32...
"In order to keep temperature and humidity at acceptable levels, you
are advised to ensure that forced airflow is provided across the
drive".
"Depending on the type of installation, the airflow may be as low as
0.03m3/min (1ft^3/min through the drive, or 0.3mm (0.01in) of water
pressure drop. This level of airflow may be achieved by the use of a
very small fan, say 40mm (11/2in) square. Note Make sure
you do not have any unfilled peripheral slots in your system. These
may cause airflow to bypass the drive completely".


Ok...

1 cubic foot per minute of air sounds very little, but it is not...
wonder if Freecom tested their enclosure?

My early DAT drives failed due to overheating in a fanless enclosure
(PCB replaced) and dust baked onto heads (made my own externally
shuttered door) hence I am asking.

I have a choice between Freecom (HP) DAT 72 and HP DAT 72 External
USB, similar price, HP is with a fan, Freecom is without. DAT is as a
second line bulk backup re cheap media for "use once, check it
restores and stick off site". Would never use DAT as first line and
LTO too expensive for second line. DAT 160 and DAT 320 are virtually
unrepairable and more problem prone it seems from various repair
outfits, DAT 72 got the balance right re reliability (as far as DAT
can with such a flimsy design, the old CBM audio cassette was more
robust).
 
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Cydrome Leader
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      08-15-2011, 11:16 PM
js.b1 <(E-Mail Removed)> wrote:
> HP Hardware Integration... HP DDS Drives Technical Reference Manual...
> covers DAT 72... HP Restricted... hmmm...
>
> p32...
> "In order to keep temperature and humidity at acceptable levels, you
> are advised to ensure that forced airflow is provided across the
> drive".
> "Depending on the type of installation, the airflow may be as low as
> 0.03m3/min (1ft^3/min through the drive, or 0.3mm (0.01in) of water
> pressure drop. This level of airflow may be achieved by the use of a
> very small fan, say 40mm (11/2in) square. Note Make sure
> you do not have any unfilled peripheral slots in your system. These
> may cause airflow to bypass the drive completely".
>
>
> Ok...
>
> 1 cubic foot per minute of air sounds very little, but it is not...
> wonder if Freecom tested their enclosure?
>
> My early DAT drives failed due to overheating in a fanless enclosure
> (PCB replaced) and dust baked onto heads (made my own externally
> shuttered door) hence I am asking.
>
> I have a choice between Freecom (HP) DAT 72 and HP DAT 72 External
> USB, similar price, HP is with a fan, Freecom is without. DAT is as a
> second line bulk backup re cheap media for "use once, check it
> restores and stick off site". Would never use DAT as first line and
> LTO too expensive for second line. DAT 160 and DAT 320 are virtually


It sounds scary you'd settle for a technology you don't trust in the first
place. I don't trust DAT either by the way.

 
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js.b1
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      08-16-2011, 08:38 PM
On Aug 16, 12:16*am, Cydrome Leader <(E-Mail Removed)> wrote:
> It sounds scary you'd settle for a technology you don't trust in the first
> place. I don't trustDATeither by the way.


Secondary backup.
The data can be recreated (just takes time).

I went with Freecom boxed HP, brand new, very cheap.
Tapes used once, archived, drive used maybe 4 times a year.

If it were someone else's money I would be buying LTO :-)
 
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js.b1
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      08-17-2011, 07:20 PM
Interesting to note...

DAT head life is 6,000hrs.
- Lets assume 3,000hrs under real world as helican scan 4mm.
- 60GB @ 6MB/sec = 3hrs backup, 3hrs verify (6hrs).
- That is 400 backups & 100 test restores.

LTO head life is 30,000hrs.
- Lets assume 30,000hrs under real world.
- 150GB @ 40MB/sec = 1hr backup, 1hr verify (2hrs), LTO-3.
- That is 14,000 backups & 1,000 test restores.

I wonder a lot of small business are put off by LTO lack of eSATA or
USB, not just the LTO sticker price.

DAT160 & DAT320 are very unreliable and nearly uneconomic to repair
compared to DAT72 from three repair shops.
 
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SpamTrapSeeSig
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      08-17-2011, 11:50 PM
In article
<(E-Mail Removed)>,
js.b1 <(E-Mail Removed)> writes
>Interesting to note...
>
>DAT head life is 6,000hrs.
>- Lets assume 3,000hrs under real world as helican scan 4mm.
>- 60GB @ 6MB/sec = 3hrs backup, 3hrs verify (6hrs).
>- That is 400 backups & 100 test restores.


I'd be interested to know where those figures come from. HP's spec
quotes 12MB/s (uncompressed) for the current generation.

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.

There is no need for a verify pass with DAT either, unless you're
checking the software worked! The technology includes read-after-write
confirmation. If it doesn't read correctly during a backup, the device
sends an error message to the software. The only reason to verify DAT is
to confirm the software sent the correct stuff to the drive.

>LTO head life is 30,000hrs.


And your data comes from... ?

>- Lets assume 30,000hrs under real world.
>- 150GB @ 40MB/sec = 1hr backup, 1hr verify (2hrs), LTO-3.
>- That is 14,000 backups & 1,000 test restores.


Again, read-after-write, thus no need for verification.

>I wonder a lot of small business are put off by LTO lack of eSATA or
>USB, not just the LTO sticker price.


LTO was designed for servers. In the real world, USB would struggle with
the data rate, as probably would eSATA if it wasn't part of an array.
Individual disks aren't very quick. 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.

>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't DAT (and it wasn't HP's either).

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

--
SimonM
 
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js.b1
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      08-18-2011, 11:44 AM
On Aug 18, 12:50*am, SpamTrapSeeSig <(E-Mail Removed)>
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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SpamTrapSeeSig
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      08-18-2011, 01:33 PM
In article
<(E-Mail Removed)>,
js.b1 <(E-Mail Removed)> writes

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


I venture to suggest that, although they may be streaming, the source
cannot supply data fast enough. The only definitive test is to stream a
large fragment from memory (eliminates disk channel bottleneck). The
original MS Backup was OEM from Seagate software and not very quick! I
don't know how much the engine was improved with later releases; I do
know how much time I used to waste trying to get decent performance out
of it! It was remarkable how significant the software component was to
performance, although I haven't run any tests in recent years.

Recent DAT and LTO generations have a 'slow speed mode', IIRC, to
minimise scrubbing with slow hosts, but there are limits!

>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.


I asked HP yesterday on-line for the current Vol 1. so as to be able to
check their current statements. They only sent me that white paper. I
don't have a current copy, but I do have the same part number - dated
2003 and the DAT72 stuff in it is provisional.

The section in question (p.40) is largely unchanged from the original
information published with DDS-1 (there wasn't an integration guide as
such then, but from memory it is similar to the OEM tech ref manual of
the time). I suspect it was only given a cursory check when it was
updated for the 2003 release (but I still don't know what the latest
numbers are, nor if HP has made them public). The drum, incidentally,
would be replaceable on those units, although I don't know about later
models.

DDS-2 was a horrid tape formulation, incidentally, that really got
through heads quickly.

>- A large proportion of cartridges loaded are being used for the first
>time."


Actually, this gives *worse* reliability than re-using tapes as much as
possible.

The reason is that new tapes tend to have microscopic rubbish all over
them from the manufacturing processes. This is scraped off in the first
few passes through the drive, whereafter the raw error rate decreases to
a reasonably constant level, until the tape finally wears out (100-200
passes, typically). If you always put new tapes in, it can thus increase
the head wear (although since DDS-3 drives have hardware included to
clean head + tape ). Tape brand can also have a significant effect.

>Seems pretty clear to me. Covers to DAT72.


Well, it makes sense, but I think they're being very conservative (and
the MTBF is optimistic!).

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


Bear in mind, in all cases, the head life quoted is (a) conservative,
and (b) the result of statistical analysis of testing. AFAIK, it's not
derived from real life failure data, although can cause MTBF to be
reviewed.

>My first encounter with DAT was HP C1533A in 1994.


I remember it well.

>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.


Indeed so. There remains very little awareness of the issue within the
industry, partly because of the imaginary transfer rates appearing on
disk specs. It's still a problem.

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


They'll survive quite a lot of abuse. I once trod on a cartridge at a
trade show: It loaded, but I wouldn't have wanted to put it into any
backup pool! In contrast, the mechanical issues with, say, DLT were
horrid: if you dropped one on a corner from chest height onto a hard
floor, you'd break it. Don't get me started on the leaders...

>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.


DLT was always a horrible bodge. The LTO designs essentially started by
dissecting DLT and compiling a list of "we're not going to do that!"
items.

>> >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?


Oh yes. Or perhaps just "Oh!" As you say, many were input-only devices.
The mechanical designs were just nasty.

>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.


I can't speak to the dual standard ones (my experience of DDS is DDS 1
thru 4). If they are unreliable, I'm not surprised, as the geometry
would be asymmetric.

>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.


Probably. I wouldn't use a dual-gauge format personally. LTO in
comparison is brilliant, but you pay for what you get.

>It is quite possible people are using the wrong tool for the job,
>thrashing DAT160/320 when something like LTO would be more suitable.


It's a difficult one. The issue of not-streaming doesn't have any really
robust solution, although LTO is far better at 'throttling' than
predecessors. There is an argument that it's far better to use a drive
that matches the throughput of the storage subsystem, i.e. slower if
necessary.

>I suspect these could be Dell badged units bundled with servers and
>someone on the purchasing side sees a budget saving over LTO.


Dell OEMs from someone (don't know who at the moment). One of the
biggest issues with all tape drives (except in high-end library
configurations) is environment: dust kills them. If these are small
servers, the chances are they're not used in the cleanest locations.

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


I agree on that, however I'd suggest that most small business, even
these days, doesn't put a realistic value on their data. If they did,
LTO would be more prevalent as cost-effective 'insurance'.

>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.


It wasn't manufacturing tolerances as much as the propensity for tape
guides to work loose from factory settings in high-vibration
environments. Data wasn't lost, and the models concerned had the
manufacturing/alignment process altered to fix it. The issue was made
worse because of the relative success of DDS at the time - other
technologies were as bad/considerably worse, but because they weren't as
popular, the issues weren't as generally obvious. All this was around
eighteen years ago, though!

I know interchange tests between DAT manufacturers were taken very
seriously, with specimen tapes being exchanged to confirm they did what
was claimed.

Cheers,

S.

--
SimonM
 
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js.b1
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      08-18-2011, 03:55 PM
MTBF is always optimistic.

DDS-2 tape.
Interesting the formulation was horrid... I do recall people and
myself going back to DDS-1 at the time and finding it helped. DDS-2
from Imation seemed problematic with 3M labs admitting a fault with
each one I sent to them. Few hours usage, they did not say whether it
was tape or the drive (boulder baked onto head).

DDS-3 drives.
They did introduce self cleaning wipe rollers, but I recall some
drives had the threshold set too low so let the heads get dirty. It
might have been Sony or Seagate drives which tends to fit with people
throwing the towel in with DAT. Indeed this may have been true with
DDS-2 and certain tapes.

New tapes shed.
This irritates, why not add a manufacturing process to pre-wipe the
tapes and rejects bad tapes instead of shifting it onto the end user's
own physical hardware to suffer? They could double the price of "pre-
super-clean super certified media".
Some paper by Compaq said new tapes required the drive to be cleaned
every 8hrs, only after the entire tape had been used 5 times could the
drive be cleaned every 25hrs. Also it may need to be cleaned 4 times
in a row where a head clog occurred.

Tape quality.
A Compaq paper stressed bad tapes should be scrapped, as indicated by
examining the error sense code re high torque tape, head clog, end of
tape market dysfunctional etc. Tape repairers said HP tapes were the
best, with Sony & relabelled (outsourced Imation etc) decidedly
inferior. In that respect it is like CD DVD.


DDS-2 DAT actually only ever failed to recover 1 file - but did off
another tape, it just generally drove me mad with orange flashing
lights during a backup even when it had been cleaned just before.
Drive hours were very low, I think it was DDS-2 tapes which were all
3M Imation. They got returned to Imation labs who confirmed a fault,
sent replacement. Weird.

Runny green CDR actually lost more files than I want to remember -
Kodak CDR Gold, Imation, Verbatim all lost stuff as much because of
the early drives having poor calibration, poor lasers etc. Just not
worth the hassle.

Trying DVD-R recently from A-One made me run away, some would write,
some would not write.

I actually use 3 backup media; spare laptop HD, 3.5" MO, DAT 4mm. The
attraction of DAT is multiple copies are cheap (3 being the minimum)
and relatively fast compared to 3.5" MO disk swapping.

Small business does not cost backups properly.
A major brand PC in 1990 was about 1500-1900, in today's depreciated
(!) money an LTO tape drive is very little. If a business has to pay
50 people 8hrs at 10$/hr for re-entry of lost data it is 4,000$ - yet
how few businesses could actually do that and how much more is that
than an LTO drive.
Hard drives are good for backups, as long as not all carried in one
box, kept at different locations, archived properly. Still makes me
nervous re need for multiple brands, multiple models. Hard drives were
not meant for "no use for 5yrs" and are a single point of failure. You
need a lot more hard drives than people think.

Keeps the data recovery companies in business sticking new PCB & heads
in them though :-)
 
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