Date: Thu, 17 Apr 97 10:55:57 METDST From: Rob Schofield <rschof@mccomm.nl> To: freebsd-hardware@freebsd.org (Hardware list at FreeBSD) Subject: Re: Repeated UNIT ATTENTION, what is it, is this serious? Message-ID: <199704170856.KAA10442@mccomm.nl> In-Reply-To: <3.0.32.19970416150727.006ccadc@lariat.org>; from "Brett Glass" at Apr 16, 97 3:07 pm
next in thread | previous in thread | raw e-mail | index | archive | help
> The problem could be anything from a parity error to overlapping SCSI IDs > to bad termination to soft errors on the disk or tape. - or that old chestnut, a power supply that can't deal with the peak and static current requirements of so many disks/tape drives/etc. in one box. There was speak of sperating the number of drives onto two buses giving success, but no-one remarked that this could have been successful as a result of having to move the devices into a seperate box, new power supply, etc. and thereby reducing power load on the original PSU. There is also the question of power being supplied to the termination of the last device on the chain; if the end termination is being affected by a sickly power supply, then commands on the bus issued by the host at the far end could be getting "lost" or garbled when a target device cannot evaluate the voltage levels presented at it's bus connection, then either do not respond or go to UA condition as a result of what it thinks is an "illegal command" being presented. There are many reasons, unfortunately - but I would look at the power supply as it (and the drives it is powering) get nice and hot after a few hours of work, then measure the term power supply voltage on the terminator device. What does surprise me here is that from comments made, no attempt is being made by the FreeBSD driver to follow a "Soft/Hard" reset policy on miscreant devices, i.e. first issue a RESET *message* to the device and doing a command retry, then as a last resort a bus reset. Have I correctly interpreted comments here? A bus reset, whilst not that harmful, is pretty drastic action to correct the behaviour of just one (readily identifiable) device at UA! This is like tear-gassing a school bus full of kids as punishment just 'cos one peed in his pants in desperation... Rob Schofield -- Witticisms are hard to define on Monday mornings... schofiel@xs4all.nl http://www.xs4all.nl/~schofiel rschof@mccomm.nl
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199704170856.KAA10442>