*BSD News Article 57395


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From: "Leonard N. Zubkoff" <lnz@dandelion.com>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: CDROM Changers
Date: 20 Dec 1995 02:47:31 -0800
Organization: Dandelion Digital
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References: <BILLW.95Dec8181411@puli.cisco.com> <4b2q1p$796@kelewan.dandelion.com> <4b5guj$g02@elliot.ics.uci.edu> <4b5t4s$9qv@kelewan.dandelion.com> <4b8m5g$la6@elliot.ics.uci.edu>
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In-reply-to: shettich@elliot.ics.uci.edu's message of 20 Dec 1995 01:48:32 -0800

In article <4b8m5g$la6@elliot.ics.uci.edu> shettich@elliot.ics.uci.edu (Seth Hettich) writes:

  In article <4b5t4s$9qv@kelewan.dandelion.com>,
  Leonard N. Zubkoff <lnz@dandelion.com> wrote:
  >It's a CD-ROM changer.  That means it has a single reader and a mechanism
  >to automatically switch between the CD-ROMs, transparently to the host
  >except for the latency involved.  Switching from one CD-ROM to another
  >takes a few seconds, so it will certainly sound like thrashing if you
  >continually send commands that force the changer mechanism to operate.  All
  >the CD-ROMs are logically available at the same time, but not physically.

  So can you have 2 users both reading from 2 different CD's, slowly, or
  will you just get a bunch or errors?  basically, would I need to set something
  up to ensure that 2 CD's won't be read from at the same time?

I'm afraid someone familiar with how FreeBSD handles this will have to
answer this one.  Whether you'll get errors/timeouts or not depends on the
kernel, I expect.  With a long enough timeout, you can certainly have two
different users reading two different CDs slowly.  I believe the Linux
timeout for SCSI CD-ROMs was increased to 15 seconds to accommodate these
changer devices.

		Leonard