HP-UX 11i v3 Native Multi-Pathing for Mass Storage (August 2012)

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how multi-pathing works, depending on the setting of leg_mpath_enable, when an application
accesses disk17 through the legacy DSF /dev/rdsk/c5t2d4.
All lunpaths of disk17 are used when /dev/rdsk/c5t2d4 is opened while leg_mpath_enable is
set to true.
To display the current value of leg_mpath_enable for disk17, enter:
# scsimgr get_attr –D /dev/rdisk/disk17 –a leg_mpath_enable
SCSI ATTRIBUTES FOR LUN : /dev/rdisk/disk17
name = leg_mpath_enable
current = true
default = true
saved =
To clear statistics for all lunpaths of disk17, enter:
# scsimgr clear_stat -D /dev/rdisk/disk17 all_lpt
scsimgr: Cleared statistics successfully
To verify that total I/O processed on each lunpath of disk17 is now 0, enter:
# scsimgr get_stat –D /dev/rdisk/disk17 all_lpt | grep "Total I/Os processed"
Total I/Os processed = 0
Total I/Os processed = 0
Total I/Os processed = 0
Total I/Os processed = 0
To display the I/O load balancing policy applicable for disk17, enter:
# scsimgr get_attr -D /dev/rdisk/disk17 -a load_bal_policy
SCSI ATTRIBUTES FOR LUN : /dev/rdisk/disk17
name = load_bal_policy
current = round_robin
default = round_robin
saved =
To open /dev/rdsk/c5t2d4, and send 120 I/O operations to disk17, enter:
# dd if=/dev/rdsk/c5t2d4 of=/dev/null count=120
120+0 records in
120+0 records out
To verify the number of I/Os sent on each lunpath of disk17, enter:
# scsimgr get_stat -D /dev/rdisk/disk17 all_lpt | grep "Total I/Os processed"
Total I/Os processed = 40
Total I/Os processed = 40
Total I/Os processed = 40
Total I/Os processed = 40
The output shows the same number of I/O transactions are processed on each lunpath of disk17. This
is consistent with the round_robin I/O load balancing policy. In addition, the total number of I/O
transfers processed on each lunpath is greater than 120/4 because of the overhead associated with
opening a device.
You can open /dev/rdsk/c5t2d4 and transfer data even if the corresponding lunpath is not
available. In this example, the cable to the HBA with hardware path 0/2/1/0 is disconnected.
Lunpaths using this HBA are now unavailable as shown in the following ioscan output. Their S/W
state is now NO_HW.
# ioscan -kfnNC lunpath
Class I H/W Path Driver S/W State H/W Type Description
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