ADSM-L

STK9710 drive cleaning (formerly STK9714 drive cleaning)

1998-11-10 16:46:32
Subject: STK9710 drive cleaning (formerly STK9714 drive cleaning)
From: "Prather, Wanda" <PrathW1 AT CENTRAL.SSD.JHUAPL DOT EDU>
Date: Tue, 10 Nov 1998 16:46:32 -0500
Ooh, Been there, done this in GREAT DETAIL for the 9710.
Your STK rep should be seriously yelled at for not getting you the
information promptly.

As you said, ADSM is oblivious to any cleaning that goes on in the 9710,
everything occurs outboard.

You first have to enable autoclean on the front 9710 panel, as you said.
And you have to insert a cleaning tape, also using the MENU on the front
panel, so the robot
stores the cleaning tape in the special cleaning tape slot inside the 9710.

1) The threshold is set by the drive, not the 9710.
There is a tiny cable that goes back from each drive to the robot.
If the drive wants to be cleaned, it signals the robot via that cable.
The robot then mounts the cleaning tape AFTER the current data tape is
dismounted.

If your drives in the 9710 are 3490-type, they ask to be cleaned after n
feet of tape used.  Don't know what the limit is.

If you have DLT 7000's in the 9710, those drives are self-monitoring.  They
monitor signal strength from the tape heads.  If the signal amplitude gets
weak, they assume the heads are dirty and request a clean.

This means you can get bogus clean requests due to problems with the media,
or drive alignment, or drive microcode, which aren't actually due to dirty
heads.  According to Quantum, these drives should only need to be cleaned
once every several months.  We sometimes do 20 cleans a day (over 7 drives),
due to bogus clean requests.

It also means it won't help you at all to try and manually clean a drive,
since the clean requests are likely to occur at very irregular intervals.

There is no way to change the thresholds.

This design has an interesting side effect.  If you are trying to read a DLT
tape with 300000 files on it, and the drive signals a clean request at the
beginning because the heads are dirty, no clean can occur while the data
tape is still in the drive.
ADSM will get many many I/O errors trying to read that tape, and just
continue getting them as though the tape is bad.
When ADSM finally dismounts the tape, the 9710 will mount the cleaning tape.

Then if you put the tape that got all the I/O errors into another drive (or
the same one) and try to read it again, you will get no errors at all
because everything is now clean.

There is no cure for this because it is a design issue.  We have wasted MANY
MANY man hours trying to deal with it.


2) There is no record kept of when a drive was last cleaned.  Again, knowing
when the drive was last cleaned won't help you anyway with the DLT 7000.

3)  A 3490 cleaning tape you reuse 100 times, with the cleaning tape passed
from start to end each time.
A DLT cleaning tape is used differently. A DLT 7000 cleaning tape has a
limit of 20 uses.  Each time you mount the cleaning tape, it uses 1/20th of
the tape and writes a tape mark.  So on the 20th use, you are at the end of
the tape.  That also means that each clean takes longer than the last, since
you are working your way further down the cleaning tape.

On the front panel of the 9710, where you enable AUTOCLEAN, press MENU and
walk through the MENU.  One of the options is "DISPLAY CLEANING CART DATA".
And you press EXE to display the current use count on the tape.

Unfortunately, when the cleaning cart hits 20 uses, the 9710 just pops a
little message into the front panel "DLT CLEANING CART USED UP", or
something like that.  But any operation that changes that window will erase
the message, before you see it.
The use count goes back to 0 and starts over again, and the 9710 will keep
on mounting the used up cleaning tape.  It just won't do any good, since
there is no tape left to use, and the drives will still be dirty after the
cleaning tape is mounted.

That means that if the clean count is 5 when you leave on Friday and 6 when
you come back on Monday, you don't know whether  the cartridge has been used
1 time or 21 times and the 9710 is just continuing to reuse a dead cleaning
cartridge.
And you don't know whether the I/O errors you see are due to a real media
problem, or due to the fact that your cleaning cartridge got used up and you
didn't catch it.

Great design, huh?
If I had a nickel for every hour I've spent chasing I/O errors caused by
cleaning problems in the 9710, I could retire.


4) The only way I know of to force a cleaning of a particular drive is to
open the 9710 and stick the cleaning tape in yourself.

If you have further questions, please feel free to contact me directly.

***************************************************************
Wanda Prather
The Johns Hopkins Applied Physics Lab
443-778-8769
wanda_prather AT jhuapl DOT edu

"Intelligence has much less practical application than you'd think" -
Scott Adams/Dilbert
***************************************************************



> -----Original Message-----
> From: Louie, James [SMTP:LouieJ AT NABISCO DOT COM]
> Sent: Tuesday, November 10, 1998 11:32 AM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      Re: STK9714 drive cleaning
>
> We have a 9710 and have the same question.  I'm still waiting for STK to
> come back with an answer.  As far as I know, ADSM does not get involved
> with
> tape drive cleaning on the 9710.  ADSM will however report media or drive
> failures and suggest a drive cleaning (as I have found out too many
> times).
> The 9710, if set for autoclean via the front panel, is supposed to insert
> the cleaning tape after it exceeds a certain internal threshold for
> read/write errors.  My questions are 1)what are those thresholds and how
> are
> they set  2)how can I tell when a drive was last cleaned  3)how will I
> know
> when the cleaning tape is used up  4)how can I force a cleaning of a
> particular drive?
>
> Any answers would be appreciated!
>
> Thanks,
> James Louie
> Nabisco
> 973.682.7150
>
> > On Tuesday, November 10, 1998 9:58 AM, Mark Bryant ISD SWD 600 7658
> > GBZURMBT - GBZURH00 [mailto:GBZURMBT AT IBMMAIL DOT COM] wrote:
> >
> > --------------------------------------------------------------
> > -----------------
> >
> > We have installed a StorageTek 9714 DLT tape library with an
> > NT ADSM V3 server.
> > What I can't find is how to get it to use a cleaning tape on
> > its drives.
> > StorageTek are saying that its down to the software to
> > perform this but I can't
> > find any mention in ADSM of how to set this up...any ideas?
> >
> > Thanks
> >
> > Mark
> >
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