Technical data

• Provides support for XP20000/XP24000 Disk Arrays.

• Provides support for EVA iSCSI devices on RHEL5/RHEL5.1/SLES9 SP3/S LES9 SP4/SLES10/SLES10

SP1.

Softwar e Components

This section discusses the following soft ware components of Device Mapper Multipath:

• dm-multipath

kernel module -- Routes I/O and provides failover to paths and path groups.

• multipath c onﬁguration tool -- Provides commands to conﬁgure, list, and ﬂushMultipathdevices.

• multipathd daemon -- Monitors path status. When paths revert, multipathd daemon may also

initiate pat

h group switches to ensure that the optimal path group is used.

• kpartx utility -- Reads partition tables on the speciﬁ ed device and cre ates device maps over

the detected partitions. The kpar tx utility is called from hotplug whenever device maps are

created and d

eleted .

• devmap-name -- Provides a meaningful device name to udev for device maps (devmaps).

HPDM Multipath Operation

HPDM Multipath enables hosts to route I/O over the multiple paths available to an end storage unit

(LUN). A path refers to the connection from an HBA port to a storage controller port. When an active

path through which I/O happens fails, HPDM Multipath reroutes the I/O over other available paths. On

a Linux host, when there are multiple paths to a storage controller, each path appears as a separate

block device a nd hence results in multiple block devices for single LUN. HPDM Multipath creates a n ew

Multipath block device for those devices that have the same LUN WWN.

For example, a host with two HBAs when attached to a storage controller with t wo ports through a

single FC switch provides four block devices: /dev/sda, /dev/sdb, /dev/sdc,and/dev/sdd.

HPDM Multipath creates a single block device, /dev/mapper/mpath1, that reroutes I/O through

these four underlying block devices.

Introduction to HPDM Multipath