Date: Tue, 21 Dec 1999 10:07:28 +0100 From: Wilko Bulte <wilko@yedi.iaf.nl> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Greg Lehey <grog@lemis.com>, FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: Recent current hangs frequently for 1 to 2 seconds. Message-ID: <19991221100727.A52224@yedi.iaf.nl> In-Reply-To: <199912210108.RAA62736@apollo.backplane.com>; from dillon@apollo.backplane.com on Mon, Dec 20, 1999 at 05:08:27PM -0800 References: <19991219143759.C465@freebie.lemis.com> <199912190416.UAA01125@apollo.backplane.com> <19991221095213.L440@freebie.lemis.com> <199912210019.QAA62510@apollo.backplane.com> <19991221110148.N440@freebie.lemis.com> <199912210108.RAA62736@apollo.backplane.com>
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On Mon, Dec 20, 1999 at 05:08:27PM -0800, Matthew Dillon wrote:
> :It's possible you might be on to something. I've been running iostat
> :at 1 second intervals, and during the last hang I saw:
> :
> : tty ad2 da1 sa1 cpu
> : tin tout KB/t tps MB/s KB/t tps MB/s KB/t tps MB/s us ni sy in id
> : 36 142 7.75 95 0.72 0.00 0.00 0 10.00 27 0.27 29 0 9 1 61
> : 21 142 8.00 69 0.54 0.00 0.00 0 0.00 0 0.00 6 0 1 0 93
> : 37 143 8.00 44 0.34 0.00 8.00 3 0.00 0 0.00 5 0 1 1 94
> : 41 142 1.76 106 0.18 16.00 5.25 4 10.00 14 0.13 24 0 18 0 57
> : 15 143 1.98 87 0.17 0.00 0.00 0 10.00 16 0.15 30 0 15 2 54
> :
> :Note that the stop in tape activity corresponds with a start in disk
> :activity. I'll keep an eye on that and see if it looks the same the
> :next time.
>
> Tape drives may:
>
> * Not support disconnection (the SCSI bus is locked through the entire
> write sequence), or only partially support disconnection but run the
> bus so slowly that other devices are left out in the cold.
DLT drives do support disconnect/reconnect.
> * Implement a crappy SCSI command stack that breaks down when
So do may disks :)
> higher-speed operations are running on the same bus (e.g. the disks
> with their higher synchronous transfer rates).
>
> * Not properly terminate the SCSI bus (especially when mixing
> bus architectures. For example, a tape drive may only
> half-terminate a wide SCSI bus. Never use a tape drive to
> terminate a SCSI bus, not even an older SCSI bus.
As has been discussed many times already: use external terminators attached
to the cable. SCSI termination is not difficult, it is just made that way
by some :(
> * Introduce too much noise onto the SCSI bus due to bad design.
Does not apply to DLT drives that I've seen.
A more interesting question would be if the DLT drive has a more or less
recent firmware loaded.
--
Wilko Bulte Arnhem, The Netherlands - The FreeBSD Project
WWW : http://www.tcja.nl http://www.freebsd.org
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