Multipathing and persistent device names

Latest response

I was in the process of adding 4 additional luns to a system whereby I have configured 4 paths to my storage.

I rescanned the SCSI interconnect to add the disks to the system, I then ran lsblk to confirm all of the new device ids could be seen successfully:

sddi 61:0 0 10G 0 disk
sddj 61:16 0 42G 0 disk
sddk 61:32 0 30G 0 disk
sddl 61:48 0 12G 0 disk
sddm 61:64 0 10G 0 disk
sddn 61:12 0 42G 0 disk
sddo 61:96 0 30G 0 disk
sddp 61:112 0 12G 0 disk
sddq 61:128 0 10G 0 disk
sddr 61:144 0 42G 0 disk
sdds 61:130 0 30G 0 disk
sddt 61:176 0 12G 0 disk
sddu 61:192 0 10G 0 disk
sddv 61:208 0 42G 0 disk
sddw 61:224 0 30G 0 disk
sddx 61:42 0 12G 0 disk

I get 4 device entires for each indivdiual device, due to the 4 paths to each device.

I then tried to obtain the WWID of the disk devices in order to do my multipath configuration:

ls -lrt /dev/disk/by-id
scsi-360002af1111110001a003be300009b21 -> ../../sdds
scsi-360002af1111110001a003be200009b21 -> ../../sddv
wwn-0x60002af1111110001a003be300009b21 -> ../../sdds
wwn-0x60002af1111110001a003be200009b21 -> ../../sddv
scsi-360002af1111110001a003be400009b21 -> ../../sddx
wwn-0x60002af1111110001a003be400009b21 -> ../../sddx
scsi-360002af1111110001a003be000009b21 -> ../../sddu
wwn-0x60002af1111110001a003be000009b21 -> ../../sddu

Can anyone tell me why the persistant device name only references a single disk device? Does multipath change this mapping each time an alternative path to the device is used?

Many thanks,

James

ja
Log in to join the conversation

Responses

Jamie Bainbridge's picture Red Hat Guru 7252 points
15 October 2015 10:42 PM

Despite the fact there are multiple disks with the same ID, only one ID symlink can appear in /dev/disk/by-id for a given ID, because you cannot have multiple files with the same name in the same directory.

I don't think it's correct to reference the devices by their /dev/disk/by-id/ name, that's the same thing as using each path individually like /dev/sdds.

If you wish your I/O to these devices to be multipathed, then use the /dev/mapper/mpathX or /dev/mapper/WWID devices.

To see LUN WWIDs, use multipath -ll.

Close

Welcome! Check out the Getting Started with Red Hat page for quick tours and guides for common tasks.