How does multipath tool handle Lun remapping?

How does multipath tool handle Lun remapping?

[谢纲]

Hi,

multipath path tool use the external program, such as scsi_id in udev,
to get the id of the lun. But how does it handle the lun remapping?
For example, at first, thiere is a lun in array:lun1, it is mapped to
host with lun id 11. On the host, I use the multipath program to
generate a multipath device for this lun. Then I unmap lun1 and
another lun: lun2 which is mapped to the host with the same lun id 11.
In this situation, it seems that the multipath tool could not notice
that there is a change of lun even after recreate the multipath
device, is that true?

Thanks,

-- 
Xie Gang

Re: How does multipath tool handle Lun remapping?

[Konrad Rzeszutek]

On Fri, Jan 16, 2009 at 04:42:25PM +0800, 谢纲 wrote:
> Hi,
> 
> multipath path tool use the external program, such as scsi_id in udev,
> to get the id of the lun. But how does it handle the lun remapping?
> For example, at first, thiere is a lun in array:lun1, it is mapped to
> host with lun id 11. On the host, I use the multipath program to
> generate a multipath device for this lun. Then I unmap lun1 and
> another lun: lun2 which is mapped to the host with the same lun id 11.

Do you reboot the system after those unmaps/maps?

> In this situation, it seems that the multipath tool could not notice
> that there is a change of lun even after recreate the multipath
> device, is that true?

It would - as long as hte block devices get re-created/deleted
for the new/old LUNs.

> 
> Thanks,
> 
> -- 
> Xie Gang
> 
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel

Re: How does multipath tool handle Lun remapping?

[谢纲]

It make sense that multipath tool can notice that there is a
recreation of OS device. But it still depends on the external program,
such as scsi_id to get the identifier of the lun。
I looked through the scsi_id source code, found that unit serial
number might be returned if the device supported the EVPD inquery
page80. This might be the wrong infomation for multipath tool, is that
true?

Thanks,

On Sat, Jan 17, 2009 at 2:13 AM, Konrad Rzeszutek
<konrad@virtualiron.com> wrote:
> On Fri, Jan 16, 2009 at 04:42:25PM +0800, 谢纲 wrote:
>> Hi,
>>
>> multipath path tool use the external program, such as scsi_id in udev,
>> to get the id of the lun. But how does it handle the lun remapping?
>> For example, at first, thiere is a lun in array:lun1, it is mapped to
>> host with lun id 11. On the host, I use the multipath program to
>> generate a multipath device for this lun. Then I unmap lun1 and
>> another lun: lun2 which is mapped to the host with the same lun id 11.
>
> Do you reboot the system after those unmaps/maps?
>
>> In this situation, it seems that the multipath tool could not notice
>> that there is a change of lun even after recreate the multipath
>> device, is that true?
>
> It would - as long as hte block devices get re-created/deleted
> for the new/old LUNs.
>
>>
>> Thanks,
>>
>> --
>> Xie Gang
>>
>> --
>> dm-devel mailing list
>> dm-devel@redhat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
>
> --
> dm-devel mailing list
> dm-devel@redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
>



-- 
Xie Gang

Re: How does multipath tool handle Lun remapping?

[Konrad Rzeszutek]

On Tue, Jan 20, 2009 at 11:17:53AM +0800, 谢纲 wrote:
> It make sense that multipath tool can notice that there is a
> recreation of OS device. But it still depends on the external program,
> such as scsi_id to get the identifier of the lun。
> I looked through the scsi_id source code, found that unit serial
> number might be returned if the device supported the EVPD inquery
> page80. This might be the wrong infomation for multipath tool, is that
> true?

That information is correct. You can prove it yourself by running
'scsi_id -g -u -s /block/sdb' before and after the deletion. The
value will be the same.


What is not correct is the LUN number. And for that there needs
to be a deletion of the block device and a recreation of them.