HP-UX native multipathing

Efficient multipathing support on an HP-UX system that is configured for an iSCSI initiator involves several requirements and guidelines to consider.

After the iSCSI initiator is configured, the HP-UX native multipathing is statically linked with the kernel, which means no setup is required to use the multipathing support.

You must find out the pseudo device or persistent device-specific file that was created by the multipathing kernel module. If you see I/Os going through the persistent device-specific file, then HP-UX native multipathing is operating. If you do not see the I/Os going through the persistent device-specific file, then native multipathing is not operating.

For more information about configuring the HP-UX iSCSI software initiator, see the HP technical documentation website.

If you have one LUN that is exported to the HP-UX system and the initiator logs in to both targets, the LUN is accessible from the two different paths. In this case, HP-UX 11i v3 creates only one persistent device-specific file per LUN.

If you issue the # ioscan -kfnNC disk command, you see which persistent device-specific files exist, in the format of the following output:

Class     I  H/W Path        Driver S/W State   H/W Type     Description
=======================================================================
disk      4  64000/0xfa00/0x0  esdisk   CLAIMED     DEVICE       HP  DG146BABCF
                            /dev/disk/disk4   /dev/rdisk/disk4
disk      5  64000/0xfa00/0x1  esdisk   CLAIMED     DEVICE       HP  DG146BABCF
                            /dev/disk/disk5   /dev/rdisk/disk5
disk      6  64000/0xfa00/0x2  esdisk   CLAIMED     DEVICE       HP  DG146BABCF
                            /dev/disk/disk6   /dev/disk/disk6_p1  
                            /dev/disk/disk6_p2  /dev/disk/disk6_p3
disk      7  64000/0xfa00/0x3  esdisk   CLAIMED     DEVICE       HP  DG146BABCF
                            /dev/disk/disk7  /dev/rdisk/disk7
disk      9  64000/0xfa00/0x4  esdisk   CLAIMED     DEVICE       TEAC DVD-ROM 
DW-224EV /dev/disk/disk586    /dev/rdisk/disk586

The ioscan command queries the mapping combinations between LUN and lunpaths by using the persistent device-specific file:

To which legacy DSF does /dev/rdisk/disk587 map?

# ioscan -m dsf/dev/rdisk/disk586
Persistent DSF      Legacy DSF(s)
=============================================
/dev/rdisk/disk586  /dev/rdsk/c15t0d0
                      /dev/rdsk/c16t0d0

To which persistent DSF does /dev/rdsk/c5t2d4 map?
# ioscan -m dsf/dev/rdsk/c150d0
Persistent DSF      Legacy DSF(s)
=============================================
/dev/rdisk/disk586  /dev/rdsk/c15t0d0