thanks very much, mike.  gets me onto the right path, i think...

On Feb 19, 2009, at 12:19 PM, Mike Christie wrote:

> /iJesse Butler wrote:
>> I am trying to troubleshoot why a connection is popping up and down,
>> and finally staying down, with a Linux RHEL 5.2 Open iSCSI / iSER
>> initiator.
>> I see various references to "host reset", and finally one looks like
>> the following. It says it succeeded, but this time rather than IO
>> continuing, I see the "Device offlined - not ready after error
>> recovery".
>> Do we have any idea what is happening here based upon this console
>> output?  What is "host reset" meant to do, and can we tell how it
>> failed?
> Each scsi command has a timeout. You can see it in
> /sys/block/sdX/device/timeout. If a command does not complete with  
> that
> time, the scsi layer fires it's error handler, which basically asks  
> the
> driver to:
> 1. abort the taask.
> 2. if 1 fails, reset the lu
> 3. if 2 fails, reset the bus (iscsi does not do this).
> 4. if 3 fails, reset the host.
> (in newer kernels there is a 2.5 where you can reset the target).
> Software iscsi has a weird implementation where it does a host per
> session, and for the host reset we just logout the session and try to
> log in. We should to a target reset, but we do not currently due to  
> bugs.
> If we get to #4 and that fails then the scsi layer will offline the  
> devices.
> If any of 1-4 is successful in fixing the problem, the scsi layer will
> send some commands to test it out. It will normally send a TUR. If
> eventually get to #4 and the reset succeeds but the TUR fails, then
> devices will be offlined.
> So for some reason
> 1. commands are taking a long time and are timing out. I think the
> default in RHEL is 60 seconds.
> 2. For some reason the transport seems fine. We can login and out.
> 3. For some reason the TUR to test the reset is failing.
> If you do not have a scsi disk you can enable lots of scsi layer
> debugging by doing
> echo -1  > /proc/sys/dev/scsi/logging_level
> if you have other scsi or data disks in the system you probably want
> less debugging or it will be a mess.
> >

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