Partitioning Multipathed Devices; Configuring The Server For Multipathing; Configuring Mdadm.conf And Lvm.conf To Scan Devices By Uuid - Novell LINUX ENTERPRISE SERVER 10 - STORAGE ADMINISTRATION GUIDE 7-2007 Administration Manual

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5.4.2 Partitioning Multipathed Devices

Partitioning devices that have multiple paths is not recommended. However, if you want to partition
the device, you should configure its partitions using fdisk or YaST2 before configuring
multipathing. This is necessary because partitioning a DM-MPIO device is not supported.
Partitioning operations on md# devices fail if attempted.
If you configure partitions for a device, DM-MPIO automatically recognizes the partitions and
indicates them by appending p1-pn to the device's UUID, such as
/dev/disk/by-id/3600601607cf30e00184589a37a31d911p1
To partition DM-MPIO devices, you must disable DM-MPIO, partition the normal device node
(such as /dev/sdc), then reboot to allow DM-MPIO to see the new partitions.

5.4.3 Configuring the Server for Multipathing

The system must be manually configured to automatically load the device drivers for the controllers
to which the multipath I/O devices are connected within the INITRD. Therefore add the needed
driver module to the variable INITRD_MODULES in the file /etc/sysconfig/kernel.
For example, if your system contains a RAID controller accessed by the cciss driver and multipath I/
O devices connected to a Qlogic controller accessed by the driver qla2xxx, this entry would look
like:
INITRD_MODULES="cciss"
Because the Qlogic driver is not automatically loaded on start-up, add it here:
INITRD_MODULES="cciss qla2xxx"
After having changed /etc/sysconfig/kernel, recreate the INITRD on your system with
the command mkinitrd.
When you are using LILO as a boot manager, reinstall it with the command /sbin/lilo. No
further action is required if you are using GRUB.
5.4.4 Configuring mdadm.conf and lvm.conf to Scan Devices
by UUID
Strange behavior occurs if you use the device node names (such as /dev/sdc) instead of the
device's UUID. The UUID does not change by reboot or when a path is failed over. Multipathed
devices show up automatically by their UUID in the /dev/disk/by-id directory.
The default settings in mdadm.conf and lvm.conf files do not work properly with multipathed
devices. By default, both md and LVM2 scan only the physical devices, and they ignore any
symbolic links to devices and Device Mapper multipath I/O (DM-MPIO) devices. When managing
DM-MPIO devices, you want the opposite behavior, so they ignore all physical devices, and scan
only the devices listed in the /dev/disk/by-id directory.
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