Date: Mon, 20 Dec 1999 17:08:27 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Greg Lehey <grog@lemis.com> Cc: FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: Recent current hangs frequently for 1 to 2 seconds. Message-ID: <199912210108.RAA62736@apollo.backplane.com> 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>
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: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.
* Implement a crappy SCSI command stack that breaks down when
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.
* Introduce too much noise onto the SCSI bus due to bad design.
At one time or another I've been hit with all of these problems. You
may be able to work around some of them by going into the adaptec
bios config and intentionally slowing down all the devices on the bus.
-Matt
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