dave wrote:
> On Mar 19, 10:56 am, Mike Christie <micha...@cs.wisc.edu> wrote:
>> dave wrote:
>>> Can anyone tell me why the SCSI layer says the device is not ready
>>> when iscsiadm reports it is logged in?
>>> Can I manually online the device? How should I recover from here?
>> You can do
>> echo running > /sys/block/sdX/device/state
>> but you might not want to because the device may not be back.
> A disk in the Sun iscsi target server died. When a disk fails in the
> server, the iscsi target pauses all read/writes for about 1-2 minutes
> until it marks the disk as faulted, then continues normal operation
> using the rest of the RAID pool. I had tested this before and dm-
> multipath with iscsi seemed to work just fine when the iscsi target
> paused and eventually resumed, so I was just a little surprised this
> time. Usually I see timing closer to a minute between conn error and
> recovery... what are the reconnect/recovery timers of open-iscsi for
> this scenario?

First the scsi command timer would expire. You can see/set this in 
/sys/block/sdX/device/timeout (there is also a udev rule). This causes 
the scsi eh to run. That will try to abort the tasks on the device. If 
that fails we try a lu reset. If that fails we drop the sessions on the 
host and relogin (that is where the host reset messages comes from). So 
for a disk failure, we can log back in quickly because the target is 
fine. The scsi eh will then send a TUR to the device to verify it is 
back. The TUR would/could then fail quickly like you saw because the 
disk really is bad. For this when you know the disk is back online then 
you would want to manually set the state to running. Eventually 
multipathd will then set the path back online in the mulitpath device.

>>> Is this a known problem, and has it been fixed in newer open-iscsi
>>> versions?
>> Are you using a older version of the sun target?
> I am. I am running OpenSoalris SXCE build 93, which is about 8 months
> old. I'll be upgrading this soon.
>>> Mar 18 18:21:33 eq1-vz2 kernel:  connection1:0: detected conn error
>>> (1011)
>>> Mar 18 18:21:36 eq1-vz2 kernel:  session1: host reset succeeded
>> When we log back in we tell scsi-ml that we are ok.
> At what level does the connection receive an error and reset (can't
> log in to target, read/write errors, etc), and what functionality is
> needed to be considered ok? If the device wasn't really ready to be
> used again, shouldn't iscsi know this and attempt another recovery?
> I'm not particularly well versed in iscsi protocol.

iSCSI does not know this and does not really deal with the device. It 
deals with the connections/session to the target port/portal. So the 
target seems fine, and so can relog in quickly. The connections are fine 
and we can send iscsi level IOs like logins and nops to the target and 
it will respond ok. The target could tell the initiator that it is 
temporarily unavailable when we try to login again, but if it can allow 
IO to other disks while this problem on the one bad disk is going on it 
probably would not want to do this.

If the target is returning something in the TUR that indicates that the 
device is only temporarily gone, then maybe we would want to change the 
scsi layer so that instead of failing and setting the device offline 
right away it retries its eh a little later.

>>> Mar 18 18:22:16 eq1-vz2 kernel: sd 6:0:0:0: scsi: Device offlined -
>>> not ready after error recovery
>> scsi-ml will send a Test unit ready (TUR) command to check that the
>> device is ready to go. The TUR seems to be failing and so the scsi layer
>> sets the device offline.
> Is there only one TUR sent? I would have assumed a more robust
> recovery procedure here.

Only a TUR is sent to check if the aborts or resets worked.

>> I think there was some target issue and was fixed in newer ones.
>> If you can easily replicate this then you should take wireshark/ethereal
>> trace and send the trace here so we can see why the TUR failed and make
>> sure it is not our fault before you go to the trouble of updating.
> I'll see what I can do to get a wire trace next time I have an
> opportunity to intentionally hiccup the iscsi target.

You probably do not need to worry about this. It is working like expected.

But if you could get a trace we can see what the TUR is failed with and 
maybe see if we can add some code so that if the device is telling us it 
is only a temporary problem then we do not fail right away.

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