[dm-devel] Re: [PATCH] dm mpath: Try recover from I/O failure by re-initializing the PG if device is running on one path

[Kiyoshi Ueda]

Hi Babu,

On 2009/04/22 2:06 +0900, Moger, Babu wrote:
> Hi Kiyoshi,
> 
>    Thanks for your comment.
> 
> 
>> -----Original Message-----
>> From: Kiyoshi Ueda [mailto:k-ueda at ct.jp.nec.com]
>> Sent: Monday, April 20, 2009 8:07 PM
>> To: Moger, Babu
>> Cc: 'dm-devel at redhat.com'; linux-scsi at vger.kernel.org; Chauhan, Vijay;
>> 'sekharan at us.ibm.com'
>> Subject: Re: [PATCH] dm mpath: Try recover from I/O failure by re-
>> initializing the PG if device is running on one path
>>
>> Hi Babu,
>>
>> On 2009/04/21 3:05 +0900, Moger, Babu wrote:
>>> This patch introduces the mechanism to recover from I/O failures by
>>> re-initializing the path if the device is running on only one path.
>>>
>>> Problem: Device mapper fails the path for every I/O error. It does not
>>> care about the type of error. There are certain errors which can be
>>> recovered by re-initializing the path again. I have seen this problem
>>> during my testing on rdac device handler. I have observed I/O errors
>>> when there is a change in Lun ownership. When Lun ownership changes
>>> device will return back with check condition with
>>> sense 0x05/0x94/0x01(SK/ASC/ASCQ -meaning Lun ownership changed).
>>> Currently, device mapper fails the path for this error and eventually
>>> this will lead to I/O error. We don't want to see I/O error for this
>>> reason.
>>
>> Shouldn't we handle this type of device error inside device handler?
> 
> The current error in question requires re-activation of the path.
> We already have a code to handle this scenario in device handler.
> But, the problem is the return status does not go to DM layer.
> The return status gets lost in scsi layer. For DM layer all the errors
> are -EIO. Any thoughts from your side.

Oh, I missed the point and I thought that re-activating the path
in your device handler was enough for the error.
Currently, I have no idea to handle your case only in dm without
seeing I/O error.

By the way, who did change the ownership when the device was running
with one path in your testing?  I can't see why such case happened.

Thanks,
Kiyoshi Ueda