Thanks Sheelagh.

Regards,
Eric Tang

---------------------- Forwarded by Eric KF Tang/Hong Kong/IBM on
18-02-2000 18:33 ---------------------------
18-02-2000 18:33 ---------------------------

Sheelagh Treweek <sheelagh.treweek AT computing-services.oxford.ac DOT uk> on
18-02-2000 17:20:57

Please respond to Sheelagh Treweek
      <sheelagh.treweek AT computing-services.oxford.ac DOT uk>

To:   ADSM-L AT VM.MARIST DOT EDU
cc:    (bcc: Eric KF Tang/Hong Kong/IBM)
Subject:  Re: Tape Sharing




Eric,

I think the microcode prevents an access to the device from one server
inadvertently interrupting the current activity of the drive on another
server. So, fairly fundamental and low-level.  Without the autoshare
microcode it really isn't safe to have a drive marked as 'online' to
more than one *sm server at a time.  In effect it returns 'unavailable'
to an enquiry to use the drive when it is busy.

What the *sm share option does is make *sm go out to the drive and check
the status before assigning it.  So you can have the drive 'online' to
two servers and checks will be made.

As to *sm code levels, I think the feature came in at 3.1.2.40?  It is
definitely in 3.1.2.42 and 3.1.2.50+.

I haven't specifically tested what happens if a drive is in use on one
server and another which has it online is rebooted - I would hope that
there would be no problem.  The microcode should ensure that the drive
activity is not interrupted.

It would really need someone in development to explain this absolutely
correctly, this is just my understanding of what is happening.

Hope this helps, Sheelagh
------------------------------------------------------------------------
Sheelagh Treweek                   Email: sheelagh.treweek AT oucs.ox.ac DOT uk
Sheelagh Treweek                   Email: sheelagh.treweek AT oucs.ox.ac DOT uk
Oxford University Computing Services           Tel:   +44 (0)1865 273205
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