> Ah if your disk are using write back cache then you are going to hit 
> some problems. So if you see this in /var/log/messages when you loging:
> kernel: sd 9:0:0:1: [sdb] Write cache: enabled,
> then later when you run iscsiadm to log out you see:
> kernel: sd 9:0:0:1: [sdb] Synchronizing SCSI cache
> Then you are going to hit problems due to the scsi sysfs interface 
> changing on us. iscsiadm is going to hang. IO is going to hang. You 
> basically have to reboot the box by hand.


Are you sure about this? When the sysfs entries are deleted (during the 
iscsiadm logout phase), the SCSI ml finishes all of the I/Os and the last
operation is sending the SCSI Cache command. Wouldn't that quiesce I/O ? Granted
this means doing these steps which are outside the normal iscsiadm:
 1). flush dirty pages (call 'sync')
 2). delete the sysfs entries (echo 1 > /sys/block/sdX/device/delete)
 3). wait until /sys/class/scsi_host/hostZ/host_busy reaches zero
 4). iscsiadm -m logout

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