Hi Jeffry,

> On Tue, 20 Dec 2005 17:57:30 +0000, John Hearns
> <[log in to unmask]> wrote:
> 
> >
> >I've set up LinuxHA and high availability NFS, and would prefer to use a
> >dual-port SCSI array for this, or a SAN setup.
> >Remember to mirror the lock files between the two systems also.
> >
> >I've used DRBD, but would advise monitoring if it is working, ie. if it
> >fails on the recipinet machine the mirror will be out of sync and you
> >need to restart it.
> 
> Speaking of SAN's, has anyone gotten the multipath feature in SL42 
> to work? We have an IBM blade equipped with a dual-port Qlogic 
> controller connected through two independent fabrics to a 
> DS400/Adaptec array with a dual-port controller.  fdisk -l shows two 
> paths to every logical array, ie. each disk shows up twice.  The 
> instructions make it look easy (comment everything out from 
> /etc/multipath.conf, start up multipathd and away you go). Running 
> multipath -v2 -l shows nothing.  multipath -v3 shows that it sees 
> all of the devices but I don't know how to decipher where it is 
> going wrong (I'd attach the output but I'm typing this from home). 
>  Ideas? -- Jeff

I have been building various RHEL4 U1 blades which boot off SAN. The SAN is an
HP XP12000 array.

I used the HP Rapid Deployment Pack to build them.

The gotcha for me was when I installed the HP Proliant Support Pack, which
installs the "updated" qlogic driver (but defaults to single-pathed mode).
When the PSP performs this install, it not only install the qla2x00 RPM, but
also installs the fibreutils RPM which allows you to use lssd etc to see /
view your qlogic controllers. It also builds a new /boot/initrd... file.

This was turned out to be the problem for me. When the SAN guys enabled
multipathing on the SAN, I could see two disks (/dev/sda and /dev/sdb) when I
should be seeing only /dev/sda (but in multipathed mode). When seeing two
disks, the "LABEL=/boot" command in the fstab file would conflict as "both
disks" have the same label.

When I finally figured out that the HP PSP was not installing the qla2x00
driver in failover mode, then I made sure it did and the next time I booted
only /dev/sda would show up, even though two paths were seen.

My point is, because initrd is loaded at the very early stages of the kernel
boot process, then if initrd has single-pathing enabled (via the driver that's
built into it), you'll see two disks. Everything after that will cause you
problems.

Michael.