ADSM-L

Re: I/O errors on copy pool volumes

1997-07-01 10:35:27
Subject: Re: I/O errors on copy pool volumes
From: "Prather, Wanda" <PrathW1 AT CENTRAL.SSD.JHUAPL DOT EDU>
Date: Tue, 1 Jul 1997 10:35:27 -0400
Hi Tom,

I do not agree with your presumption that the copy storage pool volume
will suffer an I/O error if the primary volume does.

First, I have worked with 3490E drives a long time, and they are are
ENORMOUSLY reliable.  We move gigabytes of data per day, and see less
than 1 hard I/O error per month (we have 10 mainframe-attached IBM 3490
E's and 6 RS6000-attached STK 3490E compatible drives).

Read errors can occur due to a mechanical drive error.  But it is
usually because the tape has been damaged at some point (stretched or
crumpled) or the tape was VERY old or had a bad spot to start with.
This does happen, but it should happen VERY seldom, and there is no
particular liklihood that the copy pool tape would suffer the same
damage at the same time.

Also, when ADSM creates a copy pool tape, it is a logical copy, not a
physical one.  ADSM copies each file, rather than making an exact
physical duplicate of the tape.  My primary pool is collocated, and the
copy pool is not, so there is not even a 1-to-1 correspondence between
the contents of the primary and copy pool tapes, so there is no reason
to think one will be damaged if the other is.

If you are getting read errors on a tape, either:
        1) there is physical damage to the tape, in which case the copy
storage pool tape is a suitable recovery mechanism, or
        2) there is a logical error because ADSM put the data on the
tape incorrectly, in which case you have a reportable, fixable problem.

I suggest that next time you have the problem, DO try to recover the
file from the copy pool tape.  If you can't, you should report the
problem to IBM ADSM support at once, because that should never happen.

If you can recover from the copy pool tape, only the primary tape is
bad.  If it happens often, you should talk to your Customer Engineer.
He/she should be able to determine exactly what caused the I/O error;
whether you have a batch of bad tapes, or a drive maintenance problem.
You should not be having consistent problems with a 3490E.

Good luck!


 =======================================================================
Wanda Prather
Johns Hopkins Applied Physics Lab
301-953-6000 X8769
wanda_prather AT jhuapl DOT edu

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

> ----------
> From:         Tom Denier[SMTP:tom AT WAL6000B.UDC.UPENN DOT EDU]
> Sent:         Monday, June 30, 1997 4:40 PM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      I/O errors on copy pool volumes
>
> Our site uses a copy storage pool which is stored offsite for disaster
> recovery purposes. We have three 3490E drives, which are used to read
> and write volumes for both the copy storage pool and a primary storage
> pool kept onsite. We have occasionally attempted to read files from a
> primary storage poor cartridge and had the attempt fail with I/O
> errors.
> When this happens to a primary storage pool volume we have the option
> of recovering files from the copy storage pool. However, a copy
> storage
> pool volume is presumably just as likely as a primary storage pool
> volume to suffer this kind of problem. If we ran into such a problem,
> it would probably be after a disaster at a regular site, so that we
> would not have the option of retrieving copies of the unreadable files
> from somewhere else. How are other sites dealing with this concern?
>
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