Chapter 5. Managing Multipath I/O for Devices / 5.12. Using Multipathed Devices | ||||
|---|---|---|---|---|
 | 5.11. Scanning for New Partitioned Devices without Rebooting | 5.13. Viewing Multipath I/O Status |  | |
Chapter 5. Managing Multipath I/O for Devices / 5.12. Using Multipathed Devices | ||||
|---|---|---|---|---|
| 5.11. Scanning for New Partitioned Devices without Rebooting | 5.13. Viewing Multipath I/O Status | | |
Multipathed devices can be used directly, with LVM2, with EVMS, and with mdadm.
If you want to use the entire LUN directly (for example, if you are using the SAN features to partition your storage), you can simply use the /dev/disk/by-id/xxx names directly for mkfs, fstab, your application, etc.
If the user-friendly names option is enabled in the /etc/multipath.conf file, you can optionally use the /dev/mapper/mpathn device name because this name is aliased to the devices ID. For information, see Section 5.4.5.3, “Configuring User-Friendly Names or Alias Names in /etc/multipath.conf”.
To make LVM2 recognize the multipathed devices as possible physical volumes, you must modify /etc/lvm/lvm.conf. It is important to modify it in a way that it does not scan and use the physical paths, but only accesses the multipath I/O storage through the multipath I/O layer. To do so, change the filter and types entry in /etc/lvm/lvm.conf as follows:
filter = [ "a|/dev/disk/by-id/.*|", "r|.*|" ] types = [ "device-mapper", 253 ]
This allows LVM2 to scan only the by-id paths and reject everything else. If you are also using LVM2 on non-multipathed devices, make the necessary adjustments to suit your setup.
The mdadm tool requires that the devices be accessed by the ID rather than by the device node path. Therefore, the DEVICE entry in /etc/mdadm.conf should be set as follows:
DEVICE /dev/disk/by-id/*
This is the default handling in SUSE Linux Enterprise Server 10 and later.
In SUSE Linux Enterprise Server 10, the kpartx software is used in the /etc/init.d/boot.multipath to add symlinks to the /dev/dm-* line in the multipath.conf configuration file for any newly created partitions without requiring a reboot. This triggers udevd to fill in the /dev/disk/by-* symlinks. The main benefit is that you can call kpartx with the new parameters without having to reboot the server.
In SUSE Linux Enterprise Server 9, it is not possible to partition multipath I/O devices themselves. If the underlying physical device is already partitioned, the multipath I/O device reflects those partitions and the layer provides /dev/disk/by-id/<name>p1 ... pN devices so you can access the partitions through the multipath I/O layer. As a consequence, the devices need to be partitioned prior to enabling multipath I/O. If you change the partitioning in the running system, DM-MP does not automatically detect and reflect these changes. The device must be reinitialized, which usually requires a reboot.
