Hi Hertha/Gerrard/anyone, SAN disk partitions device files changes with each reboot

Hi Hertha/Gerrard/Anyone else,


Thanks for the previous excellent replies to my questions.

Something new just surfaced with the NetApp SAN disks partitions
that are presented to our RHES 4.6 :

The current mappings on 1st server is :
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath0 -> ../dm-2
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath1 -> ../dm-5
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath2 -> ../dm-3
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath3 -> ../dm-4
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath4 -> ../dm-1
lrwxrwxrwx 1 root root 7 May 22 15:36 mpath5 -> ../dm-0

& "multipath -ll" gives :

mpath0 (360a98000567244396334493370345055)
[size=5 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [active]
\_ 8:0:2:5 sds 65:32 [active]
\_ 8:0:3:5 sdy 65:128 [active]
\_ round-robin 0 [enabled]
\_ 8:0:1:5 sdm 8:192 [active]
\_ 8:0:0:5 sdg 8:96 [active]

mpath1 (360a9800056724439633449336c786d69)
[size=5 GB][features="1 queue_if_no_path"][hwhandler="0"]
\_ round-robin 0 [active]
\_ 8:0:2:4 sdr 65:16 [active]
\_ 8:0:3:4 sdx 65:112 [active]
\_ round-robin 0 [enabled]
\_ 8:0:0:4 sdf 8:80 [active]
\_ 8:0:1:4 sdl 8:176 [active]

On another Linux server (with cluster script /etc/init.d/o2cb_start.sh
started),
/dev/mpath/mpath0 or mpath1 or ... mpathx completely maps to different
minor devices /dev/sd...

So we mounted on server 1 a partition (formatted as ocfs using ocfs2console)
first & create a test file on it & then on server 2, we mount
mpath0/.../mpathx
one after another to see which of it has the test file on it to identify it.

We then put in vfstab the /dev/mpath/mpathx & mountpoint for each server
that we have determined the hard way.

Alas, after we rebooted both the servers, all the mappings became different
ie on server 1 where mpath0 ->../dm-2 became mpath0 ->../dm-4 after reboot
& on server 2 where mpath0 ->../dm-1 became mpath0 ->../dm-3 after reboot.

Oracle told us to use /dev/mapper/mpathx - this appears to be more reliable
(ie it's fixed to a specific partition regardless of how many reboots are
done).

Can someone explain what's the differences between
/dev/mpath/mpathx & /dev/dm-x & /dev/mapper/mpathx

Or I've not completely installed all the required stuff from NetApp on our
Redhat servers yet that triggers this?


Thanks
U
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