[dm-devel] an interesting note on LUN coalescing

[Stewart, Sean]

Hi Brian,

I responded to your other email before I saw this one, but I wanted to
see if I could help, here, too. 

On Thu, 2014-05-15 at 09:35 -0700, Brian Bunker wrote:
> I have added a line to multipathd/main.c to see if I could get some more information when the dm device gets the wrong LUN’s underneath. So I have a dm device:
> 
> 3624a9370c90d0d631ef8783e00010004 dm-2 PURE,FlashArray
> size=500G features='0' hwhandler='0' wp=rw
> `-+- policy='round-robin 0' prio=0 status=active
>   |- 3:0:0:3 sdav 66:240 active undef running
>   |- 0:0:0:3 sdbc 67:96  active undef running
>   |- 6:0:0:3 sdbt 68:112 active undef running
>   |- 5:0:0:3 sdbu 68:128 active undef running
>   |- 7:0:0:1 sdal 66:80  active undef running
>   |- 2:0:0:1 sdb  8:16   active undef running
>   `- 4:0:0:1 sdk  8:160  active undef running
> 
> I can see that when sdk is added to the dm, it is added to a dm ending in 004, but the serial number of sdk clearly ends in 002:
> 
> May 15 05:09:55 rb9init4 multipathd: sdk: add path (uevent)
> May 15 05:09:55 rb9init4 multipathd: 3624a9370c90d0d631ef8783e00010004: load table [0 1048576000 multipath 0 0 1 1 round-robin 0 7 1 66:240 1 67:96 1 68:112 1 68:128 1 66:80 1 8:16 1 8:160 1]
> May 15 05:09:55 rb9init4 multipathd: sdk path added to devmap 3624a9370c90d0d631ef8783e00010004
> May 15 05:09:55 rb9init4 multipathd: sdk [8:160]: path has a serial C90D0D631EF8783E00010002
> 
> I am printing out pp->serial to get the serial number of sdk. 

pp->serial actually plays no part in determining the multipath device.
It is queried from VPD page 0x80, via the function get_serial, whereas
the wwid is obtained from VPD page 0x83, through the function get_uid().
The pp->wwid attribute ultimately is what it compares to determine the
multipath device.

Perhaps when you do this, we should check what the device reports as the
wwid in inquiry page 0x83?  If you have sg3_utils on your system, you
can do that through sg_vpd -p 0x83 <device>.  I'd be interested in
knowing if the page 0x83 and the serial in 0x80 are disagreeing at the
time it's being queried by multipathd..


Thanks,
Sean Stewart