Labeling Multipath drives

[Mark Komarinski]

Kenny Lussier wrote:
>
>
> This is true. For example, in /dev/mapper there is a device called 
> 350002ac00092072a1.  I can label the device, but that also creates 
> labels on what the OS sees as /dev/sdc, /dev/sdd, /dev/sde, /dev/sdf, 
> /dev/sdg, /dev/sdh, /dev/sdi, and /dev/sdj, so a mount fails.  The SAN 
> doesn't come with client-side multipathing software. That is really up 
> to the OS vendor. In this case, I am using device-mapper-multipath on 
> RHEL5.3AP (w/ their clustering suite) with a 3Par SAN. The SAN is 
> presenting all of the paths to both systems simultaneously. That isn't 
> a problem. And, if I wanted to use GFS to have the disk mounted to 
> both servers simultaneously, then that would work just fine. But, I 
> can't have the disk mounted on more then one system at any given time.
>
>
I know the problem since I just did this across 4 systems for an Oracle 
install.  We're using EMC gear, so I wound up using (and paying for) the 
EMC PowerPath software, which Does The Right Thing and presents disks as 
/dev/emcpower? and you can then have failover between FC connections.  I 
even have some udev rules to set ownership correctly.  The /dev/sd? 
disks still appear, but you don't want to use them directly for the 
reasons you mentioned.

I did a quick check on using device mapper, but I can't guarantee how 
disks appear from the SAN and DM appears to rely on using the /dev/sd? 
names to know where things go.  Between that, the ease of use of 
PowerPath, the fact I wasn't paying for it, and I didn't have time to 
learn DM, I went with PowerPath.  I think that's the clustering software 
that was referred to earlier.

If you find a way to use DM in this manner, I'm interested to know your 
results and how you set this up.  I'm also using RHEL 5.3.

-Mark