[rhelv6-list] RHEL6 booting issue with SAN

[Phil Meyer]

On 05/13/2011 01:26 AM, Amrish Parikh wrote:
>
> Hi,
>
> I am facing very weird issue on RHEL6 when SAN cable/Luns are attached.
>
>

As Eugene alluded to in the link provided, using multipath for 
persistent naming is very useful.

Here, we use many iscsi LUNs per server, and they must have predictable 
and persistent names.

We use bonded interfaces, so we don't need multipath for performance, 
but it has much more to offer than simple network load balancing and 
fail-over.

By taking advantage of multipath, we can force order into a dynamic 
environment.

Multipath allows us to ignore the /dev/sd?? entries all together, and 
use names that we define and have complete control over.

A small sample of ours:

# cat /etc/multipath.conf
#
defaults {
         user_friendly_names yes
         path_grouping_policy    multibus
         max_fds                 2048
}
multipaths {
         multipath {
                 wwid            36090a068706be755e8d694a95a010040
                 alias                   008917
         }
         multipath {
                 wwid            36090a068706bd72fc2d6f4685a01b046
                 alias                   008948
         }
}

We get the wwid in our scripts from multipath when the drive is first 
enabled.

We then generate a common name based upon our account IDs to give it a 
friendly name, and generate entries as you see above.  A multipath -r 
makes the dev entries in /dev/mapper.

Thus I can simply: ls /dev/mapper
and see all accounts on this server.  Very handy.

For internal hard drives, the advice to use uuid is a sound one.  You 
should not need to specify /dev/sd?? in fstab or in the boot command.

Good Luck!