Date: Wed, 16 Apr 1997 15:07:36 -0600 From: Brett Glass <brett@lariat.org> To: pete@sms.fi, kallio@cc.jyu.fi Cc: hardware@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: Repeated UNIT ATTENTION, what is it, is this serious? Message-ID: <3.0.32.19970416150727.006ccadc@lariat.org>
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In SCSI-speak, a "unit attention" condition means that a device was reset, was powered up, or had a serious error. The host is notified of the condition not when it occurs but only when it tries to send a command to the device -- which might be quite some time later. The command is rejected, but usually succeeds when it's retried. This is a hack that was added to SCSI because there was no easy way for a peripheral to notify the host right away when an error occurred. The problem could be anything from a parity error to overlapping SCSI IDs to bad termination to soft errors on the disk or tape. --Brett
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