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Date:      Wed, 1 Dec 1999 08:28:10 -0500 (EST)
From:      David Gilbert <dgilbert@velocet.ca>
To:        stable@freeBSD.org
Subject:   vinum experiences.
Message-ID:  <14405.8810.777783.992833@trooper.velocet.net>

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While I'm still chasing the memory corruption bug in vinum, I have a
couple of observations.

1. Removing a device (at least, with the ahc controller) locks the bus 
even though I have a RAID hot-swap ready chassy (that properly
isolates the bus between commands).  In my test, I had a completely
quiet SCSI bus when I removed one of the drives.  I then wrote to the
RAID array.  I got:

Nov 30 18:31:51 raid1 /kernel: (da8:ahc1:0:11:0): Invalidating pack
Nov 30 18:31:51 raid1 /kernel: raid.p0.s6: fatal read I/O error
Nov 30 18:31:51 raid1 /kernel: vinum: raid.p0.s6 is crashed by force
Nov 30 18:31:52 raid1 /kernel: vinum: raid.p0 is degraded
Nov 30 18:31:52 raid1 /kernel: d7: fatal drive I/O error
Nov 30 18:31:52 raid1 /kernel: vinum: drive d7 is down
Nov 30 18:31:52 raid1 /kernel: raid.p0.s6: fatal write I/O error
Nov 30 18:31:52 raid1 /kernel: vinum: raid.p0.s6 is stale by force
Nov 30 18:31:52 raid1 /kernel: d7: fatal drive I/O error
Nov 30 18:31:52 raid1 /kernel: biodone: buffer already done
Nov 30 18:31:52 raid1 /kernel: (da8:ahc1:0:11:0): Synchronize cache failed, status == 0x4a, scsi status == 0x0
Nov 30 18:33:16 raid1 /kernel: (da8:ahc1:0:11:0): lost device
Nov 30 18:33:16 raid1 /kernel: (da8:ahc1:0:11:0): removing device entry

... I got more than one of the Synchronize cache failed.  the "lost
device" was when I "camcontrol rescan 1"  ... I did do a "camcontrol
reset 1", but it didn't affect things.

The net result is that SCSI bus 1 was wedged after this.  I would
conjecture that removing a device (and running with this device
removed is precisely what the chassy was designed to do) should not
wedge things.

In fact, since the camcontrol rescan 1 was successful, I suggest that
it was cam, not the ahc driver that was somehow wedged.

2. It's not obvious how to replace a dead drive with vinum.  I have
tried several times to perform this action without success.  Vinum
attach says it should do it.  It refuses.

It would appear that vinum can currently only be backed up when it
fails (because the degraded RAID-5 still works) because adding a new
drive to the system fails.

Dave.

-- 
============================================================================
|David Gilbert, Velocet Communications.       | Two things can only be     |
|Mail:       dgilbert@velocet.net             |  equal if and only if they |
|http://www.velocet.net/~dgilbert             |   are precisely opposite.  |
=========================================================GLO================


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