ADSM-L

Re: Planning for tape requirements for MVS

1998-02-19 14:10:42
Subject: Re: Planning for tape requirements for MVS
From: "Wendrock, Richard O" <wendrro AT TEXACO DOT COM>
Date: Thu, 19 Feb 1998 13:10:42 -0600
Good points Jerry and thanks... We are thinking about bringing in 4 or 5
Magstar tape drives to improve collocation and reduce reclamation
processing.  In that case we would not want to share those drives with other
work... Thus the concern about the reasonable number to order...
Regards,



> ----------
> From:         Jerry Lawson[SMTP:jlawson AT THEHARTFORD DOT COM]
> Sent:         Thursday, February 19, 1998 1:37 PM
> To:   ADSM-L AT VM.MARIST DOT EDU
> Subject:      Planning for tape requirements for MVS
>
> ---------------------------- Forwarded with Changes
> ---------------------------
> From: INTERNET.OWNERAD at SNADGATE
> Date: 2/19/98 9:17AM
> To: Jerry Lawson at ASUPO
> *To: *ADSM-L at SNADGATE
> Subject: Planning for tape requirements for MVS
> --------------------------------------------------------------------------
> -----
> Interesting questions - I'll try to answer them as best I can.
>
> First of all, last year I had some issues with MVS tape allocation, and
> ran a
> short survey here.  One of the questions I asked was "do you dedicate tape
> drives to ADSM on an MVS system.   The answer was a resounding "NO" - only
> one
> person (out of 25) did, and he was only doing it on one of his several
> ADSM
> systems.
>
> ADSM will use dynamic allocation to get a tape drive, and as such, when he
> needs
> one, will go to the head of the queue.  This is why most people let MVS
> get the
> drives and manage them for him.  I know at my shop, ADSM will use drives
> in
> bunches - a migration for example - we run 4 parallel tasks - so we would
> need 4
> drives.  I wouldn't want to dedicate 4 drives all of the time to ADSM.
>
> There is a priority among ADSM tasks - I don't remember what it is, but it
> is
> somewhat logical, as I recall - for example, a DB backup will preempt a
> tape
> reclaim, etc.
>
> Within ADSM, on the device level, you can control the number of tape
> drives ADSM
> will take - for example, If you don't want his use of drives to exceed 4
> at one
> time, you can set this limit, and then processes will wait until the
> devices
> become available.  Sort of lets you be politically correct.
>
> As far as when does he release a tape drive, there are a couple of answers
> here
> too.  First there is a mount retention period that you can set - this
> allows
> ADSM to hold a drive for a period of time after the task is finished with
> a
> tape.  The idea is that a lot of time the same tape will be needed again.
> This
> is most true in restores, where a customer might do a few files at a time.
> If,
> for example, you set mount retention at 5 minutes, and a user restores a
> few
> files, when the restore is finished, the tape will be held on the drive
> for 5
> minutes before it is released.  If the user wants some more files before
> the 5
> minutes, and they are on the same tape, the process will start again
> immediately.  This is obviously of more value on a manual tape system,
> than it
> is on a robot driven system.
>
> The other answer to your question has to do with end of reel processing.
> ADSM
> does not follow a typical MVS paradigm here.  The intent of the design is
> to
> speed the process, and so at end of reel, rather than wait for a
> rewind/unload
> of the drive before a new mount on the same device, ADSM will ask for a
> new
> mount on a different device (assuming you aren't at the mount limit,) and
> will
> then issue the unload/rewind.   This works fine until MVS runs out of
> drives,
> and then the fun can start - ADSM will ask for a mount, he is under his
> mount
> limit, so he expects that they will be available, but they are not.  MVS
> will
> put him at the top of the queue, but in the mean time, the old drive sits
> and
> waits - no unload is issued.  Depending on your system, this may or may
> not
> occur very often, just be aware.
>
> Hope this helps
>
> Jerry Lawson
> jlawson AT thehartford DOT com
>
> ______________________________ Forward Header
> __________________________________
> Subject: Planning for tape requirements for MVS
> Author:  INTERNET.OWNERAD at SNADGATE
> Date:    2/19/98 9:17 AM
>
>
> I am trying to determine how many tape drive we will need for ADSM on MVS.
>
> How does ADSM manage tape drives on MVS?
>
> Is there a priority amongst ADSM subtask?  Does a request for recover
> carry
> a higher priority over backup?
>
> When does ADSM release a tape drive? (at end of tape or end of task)
>
>
> Regards,
>
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