hot-swap problems with Adaptec AIC-7902 (aic79xx)

[Andrea Carpani <andrea.carpani@criticalpath.net>]

Hi everybody,
here are some issues I'm having with my system dealing with
hot-swapping.

The box is a Tyan GX28 (B2881) B2881G28U4H with 4 Hot-swap U320 SCSI
bays. SCSI controller is Adaptec AIC-7902 dual channel Ultra320 SCSI.

# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: FUJITSU  Model: MAP3735NC        Rev: 0108
  Type:   Direct-Access                    ANSI SCSI revision: 03
Host: scsi0 Channel: 00 Id: 01 Lun: 00
  Vendor: FUJITSU  Model: MAP3735NC        Rev: 0108
  Type:   Direct-Access                    ANSI SCSI revision: 03

Linux kernel 2.6.12.3 (no patches).

I have 2 drives single partition set up as a single md0 software
mirrored raid device (xfs filesystem). I set /dev/sdb1 as faulty and
remove it from the array.

I then want to hot-swap the drive with another one.

echo "scsi remove-single-device 0 0 1 0" > /proc/scsi/scsi

removes it and 

cat /proc/scsi/scsi

shows this. If I physically swap the drive (with a different Maxtor one)
and issue

echo "scsi add-single-device 0 0 1 0" > /proc/scsi/scsi

nothing happens (syslog: 
Aug 24 12:53:48 localhost kernel: scsi0: ILLEGAL_PHASE 0x80
Aug 24 12:53:48 localhost kernel: (scsi0:A:1:0): Abort Message Sent)
and the new drive appears in /proc/scsi/scsi only after a second "echo"
command (I assume this is a power-up delay).

At this point I'm not yet adding the drive to the mirror. The problem is
that if I repeat the last steps more than once (remove-single-device,
swap the drives again, add-single-device) I get the following error on
the console and everything freezes

I/O error in filesystem ("md0") meta-data dev md0 block 0x44308c4
("xlog_iodone") error 5 buf count 1024
Filesystem "md0": Log I/O error detected.
Shutting down filesystem: md0
Please umount the filesystem and rectify the problem(s).

Which is quite strange as I'm only scsi-dealing with the sdb device and
the filesystem at this point should only be on sda.

Here are some questions:
Is it possible that the scsi level operations disturb the other drive?
Which is the correct way to hot-swap scsi disks? Am I doing something
wrong?
More often than not (but not as easily reproducible) the removal and
detection of a new drive fails and the box hangs (no console messages):
could it be a driver/board problem?
Are there well tested scsi adapters/drivers that I should use?
Which scsi debug info should I turn on to help understad the problem?


Thanks,
Andrea.

-- 
Andrea Carpani <andrea.carpani@criticalpath.net>