Multipathd device enumeration
We boot from SAN, even though the servers have local disks available. Eventually we will move towards Blades, so the experience is useful. But each server has a different number of LUNs available to it. The boot LUN is always LUN id 0. Without multipathd, this gave me /dev/sdb as the boot device. With multipathd, this gives me /dev/mapper/mpathX, where X is the number of LUNs I have. You may see the problem:
The kickstart file must list the boot drive order and designate a place to put the MBR. However, I can't think of a way to tell kickstart to use the last mpath device... I wish there'd be a way to make /dev/mapper/mpath0 the boot LUN...
Update: Well, it seems to be a limitation of multipath support in anaconda. I've booted the OEL 5.3 DVD ISO on 3 different bare metals and each server has a different number of LUNs associated with it. Other than that, they are identical.
On a machine with one boot LUN only, the device name is /dev/mapper/mapth0 and using that in kickstart works. On the second machine with 5 LUNs, the boot LUN becomes mapper/mpath4 even though the LUNs are numbered starting at zero for the boot LUN. Another machine with various sizes of LUNs, in total 7, has the same issue: the boot LUN - irregardless of its LUN id - becomes mapper/mpath7. Hence, the name of the multipathed boot device is dependent on the number of LUNs associated at boot time and not related to the LUN Id numbering set on the SAN-side (EMC DMX-3 in our case). This means you can't specify it in a general kickstart script but must make one for each machine, or only deploy onto machines with only a single boot LUN and add additional LUNs later on.