[dm-devel] Multipath ID not equal to LUN scsi ID

[Steffen Maier]

On 07/11/2017 05:49 AM, liuqing at huayun.com wrote:
> Once a new arrived LUN mapped we will do rescan by "echo '- - -' > /sys/class/scsi_host/host2/scan".

I was referring to a rescan of the scsi device,

https://www.ibm.com/support/knowledgecenter/linuxonibm/com.ibm.linux.z.lhdd/lhdd_t_fcp_wrk_rescan.html

not a scan of the Scsi_Host.
The latter likely keeps the old scsi device with its old properties 
being oblivious to the volume remapping on the storage target; it's 
about discovering new scsi devices previously not being known to Linux.

> After rescan only the scsi_id tool give the right serial id, udevadm still got the prvious one.
> I have monitor the udev event by udevadm monitor while mapping a new LUN to the host, who will reuse the original path. No add event is triggerred, only dm-X emits a change event.
> But if the original path is deleted(removed) then add event will be triggerred.
> 
> Flush the old WWID could make the WWID correct but the size is still incorrect as following. And 36005076300810eadf800000000000155 is actually 5GB.

likely same reason as above

> I built the tool using latest code and tried both attribute_id and getuid_callout. The issue exist in both configuration.
> 
> 
>> Dear list,
>> We have a FC storage and using multipathd to manager the FC paths.
>> I've met an issue in this environment. The following is how to recreate the issue.
>>
>> =======
>> 1. Map a LUN to host with LUN ID 0,
>> 2. rescan fc_host, a new path will be found by multipath.
>> 3. Unmap LUN 0.  path will failed as following.
>> [root at localhost sys]# multipath -ll
>> Jul 10 18:41:50 | sdp: couldn't get asymmetric access state
>> Jul 10 18:41:50 | sdq: couldn't get asymmetric access state
>> 36005076300810eadf800000000000156 dm-3 IBM,2145
>> size=8.0G features='2 queue_if_no_path retain_attached_hw_handler' hwhandler='1 alua' wp=rw
>> |-+- policy='service-time 0' prio=0 status=enabled
>> | `- 2:0:0:0 sdp 8:240 failed faulty running
>> `-+- policy='service-time 0' prio=0 status=enabled
>>     `- 2:0:1:0 sdq 65:0  failed faulty running
>> 4. Map another LUN which have different ID_SERIAL but with the same LUN ID(0).
>   
> Did you "rescan" the SCSI device via sysfs to let Linux know that this
> is now in fact a different device?
>   
> AFAIK, Linux decodes SCSI sense data for LUNs remapped on the storage
> target and emits a udev event, but I'm not aware of any default udev
> rule that would actually react. The kernel itself does not react other
> than creating the uevent.


-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

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