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[dm-devel] Re: Bug in multipath detecting devices

> It seems that if you have more than 26 disks/luns it will detect sdaa
> before it detects sdb (sda is the onboard raid & is blacklisted).  The
> result is that the major/minor numbers in /dev/mapper get out of order
> with the disks presented to the system.  For example:

Nobody claimed mapper devices numbers are static nor even predictible.
But their names really are.

Actually, you shouldn't trust Linux device number at all : the dynamic
device numbering idea still has fans amongst kernel developpers, I
guess ;)

> The major problem with this is that if I add another disk/lun in the
> future sdaa will change to another disk.  This is because sdaa is on the
> second port of the qlogic card and gets detected as a later device than
> before.  When multipath comes along it creates the device in /dev/mapper
> that sdaa is a member of before sdb's device is created.  As a result
> the multipath devices aren't in the same sequnce as the devices that the
> OS detects (sdb, sdc, etc).  It would be better if sdb was always
> detected before sdaa.  However, I don't see a way to do that in
> /etc/multipath.conf without blacklisting all of the sda* drives.
> Another option would be to have a user-configurable scan order, which I
> don't think exists (correct me if I'm wrong).  
The multipath assembly walks the device list as show by
"ls /sys/block/", ie alphabetically.

I still don't see the need to do it differently.


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