🚀 go-pugleaf

In article <k2.729244115@woodstock> k2@bl.physik.tu-muenchen.de (Klaus Steinberger) writes:
>pclink@cheops.qld.tne.oz.au (Rick) writes:
>
>>I was talking to a sales rep about adding a CDROM (CDR-84) to my existing SCSI
>>system (TMC885 + ST4767N), and he said that this will degrade the system
>>performance.  He said most users opt for a second SCSI card into which
>>they plug the CDROM.  Is this correct?  I thought that each device on a
>>SCSI bus worked independently of each other, and that data rate was
>>determined by the addressed device.  Am I wrong?
>
>You aren't wrong, but the sales rep said a little bit truth too.
>
>The situtation is the following:
>
>--- Good description of data transfer rate differences deleted
>--- Basically saying that CD-ROM transfers data slower than hard disks and
>--- thus consumes more available bus bandwidth than hard disks causing
>--- performance impact on heavily loaded/busy SCSI bus.
>--- I hope this doesn't butcher Klaus' description too much.

Our evaluations of the NEC 74 and 84 drives show that in most regards they are
some of the faster CD-ROM drives available.  However, they have a
serious flaw if you are puting them on a SCSI bus with other devices.  The
problem is that they don't disconnect when seeking, doing error recovery,
etc.  Since CD-ROM drives take a  L O N G  time to seek, this causes
significant performance degradation.  If you should be unlucky enough to
encounter a media error that causes a "rezero" in the drive, you will notice
that the bus is "hung" for about 3 seconds.  This is not acceptable for
multitasking systems that are trying to access other devices on the same bus.

_=_=_=_=_=
Daryl V. McDaniel			Micronetics
(503) 591-1869				Aloha Research Group
darylm@Mnet.com				Aloha, Oregon USA  97007-1640