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

name = lpt_to_lockdown

current = 0/4/1/0.0x0x500508b3009097f1.0x0

default =

saved =

Setting lunpath failure detection tunables

The mass storage subsystem monitors the I/O error statistics on lunpaths to detect failing lunpaths to

LUNs.

If the lunpath continues to see I/O errors with no successful completions for a certain time interval, the

SCSI stack takes the broken lunpath offline. This time interval value is defined by the

path_fail_secs LUN attribute:

# scsimgr get_attr -D /dev/rdisk/disk17 –a path_fail_secs

name = path_fail_secs

current = 120

default = 120

saved =

You can set this attribute to a different value as follows:

# scsimgr set_attr -D /dev/rdisk/disk17 -a path_fail_secs=100

Value of attribute path_fail_secs set successfully

Setting native multi-pathing support on legacy DSFs

Applications accessing devices through legacy DSFs can take advantage of native muti-pathing. That

means even if the lunpath corresponding to the legacy DSF is not available, the application can still

access the device if there is at least one lunpath available.

To give more control to users seeking stricter backward compatibility, for instance those using 3

party multi-pathing products with legacy DSFs, the settable attribute leg_mpath_enable enables or

disables multi-pathing on legacy DSFs.

Setting the leg_mpath_enable attribute affects multi-pathing on legacy DSFs as follows:

• If a legacy DSF is opened when leg_mpath_enable is set to true for the device, I/O transfer is

performed on all available lunpaths according to the I/O load balancing policy. An attempt to

open a legacy DSF succeeds even if the corresponding lunpath is not available.

• If a legacy DSF is opened when leg_mpath_enable is set to false for the device, I/O transfer

is only performed on the lunpath corresponding to the legacy DSF. If this lunpath becomes

unavailable, I/O transfers fail. If this lunpath is not available when the legacy DSF is opened, the

open fails.

• Changing the setting of leg_mpath_enable does not affect legacy DSFs that are already open. If

multi-pathing was enabled when a legacy DSF was opened, and leg_mpath_enable is set to

false while the legacy DSF is still open, I/O transfers continue to use all available lunpaths.

Likewise if multi-pathing was disabled when a legacy DSF was opened, and leg_mpath_enable

is subsequently set to true while the legacy DSF is still open, I/O transfers continue to use only the

lunpath corresponding to the legacy DSF.

In the SAN example used in this document, disk17 has four lunpaths to which correspond four

legacy DSFs. The legacy DSF /dev/rdsk/c5t2d4 corresponds to the lunpath with the hardware

path 0/2/1/0.0x500508b3009097f1.0x4014000000000000. The following examples illustrate