*BSD News Article 57109


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From: "Leonard N. Zubkoff" <lnz@dandelion.com>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: CDROM Changers
Date: 17 Dec 1995 20:18:01 -0800
Organization: Dandelion Digital
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References: <BILLW.95Dec8181411@puli.cisco.com> <4adn77$gsg@mark.ucdavis.edu> <DJECMK.KqA@sysadm.physics.uiowa.edu> <4aga5j$ei@kelewan.dandelion.com> <4b2hp9$cv5@elliot.ics.uci.edu>
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In-reply-to: shettich@elliot.ics.uci.edu's message of 17 Dec 1995 17:56:57 -0800

In article <4b2hp9$cv5@elliot.ics.uci.edu> shettich@elliot.ics.uci.edu (Seth Hettich) writes:

  >The Nakamichi MBR-7 also appears as multiple LUNs and automatically
  >switches disks.  No special SCSI commands are necessary with mine.

  What happens if you try to access 2 disks at the same time?

Well, there is no truly simultaneous access, of course.  The drive will
swap one CD for another whenever the SCSI command it receives is not
directed to the currently loaded CD-ROM.  If the SCSI command timeouts in
the kernel are set appropriately for the devices, then you will merely
thrash the MBR-7 if two or more processes attempt simultaneous access to
multiple CD-ROMs.  If the timeouts are too short, then you'll have lots of
failures.

		Leonard