Ignite-UX Administration Guide for HP-UX 11i (B3921-90079, October 2013)

Figure 17 Agile Multiple Path I/O Stack Addressing Model
Persistent DSF
Lunpath
hardware path
Lunpath
hardware path
Lunpath
hardware path
Lunpath
hardware path
Legacy DSF
Hardware path
Legacy DSF
Hardware path
LUN
hardware
path
LUN
The persistent DSF represents the device, regardless of its location in the I/O configuration. With
the new model, legacy DSFs and hardware paths enjoy multi-path capabilities because after device
open, I/Os use every path associated with the I/O device.
The LUN hardware path is virtualized, representing all the lunpath hardware paths to a device.
The lunpath hardware path is the path typically displayed in the Ignite user interface. Lunpath
hardware paths do not have device special files - they are associated with a LUN hardware path
and are accessed via the persistent DSF associated with a LUN hardware path. The Ignite user
interface displays the lunpath hardware path so the actual device can be discerned from it; you
cannot identify the physical device from looking at the LUN hardware path or the persistent DSF.
Sample agile addressing model values for the DSFs and paths are shown below.
Figure 18 Agile Naming Example
64000/0xfa00/0x6
LUN: WWID 0x50060b000015330f0001000000000032
Persistent DSF
Legacy DSFs Legacy Hardware Paths
LUN
Hard-
ware
Path
Lunpath Hardware Path
/dev/dsk/c9t0d1
/dev/disk/disk55
0/0/6/0/0.1.18.73.0.0.1
0/0/6/0
0.0x50060b000019bc98.0x4001
0/0/6/0
0.0x50060b000019c8a6.0x4001
0/0/10/0
0.0x50060b000019bc98.0x40010
0/0/10/0
0.0x50060b000019c8a6.0x40010
1/0/2/0
0.0x50060b000019c8a6.0x4001
1/0/2/0
0.0x50060b000019bc98.0x4001
1/0/14/0
0.0x50060b000019c8a6.0x40010
1/0/14/0
0.0x50060b000019bc98.0x40010
/dev/dsk/c11t0d1
0/0/6/0/0.1.19.75.0.0.1
/dev/dsk/c17t0d1
0/0/10/0/0.1.18.73.0.0.1
/dev/dsk/c19t0d1
0/0/10/0/0.1.19.75.0.0.1
/dev/dsk/c29t0d1
1/0/2/0/0.1.19.75.0.0.1
/dev/dsk/c27t0d1
1/0/2/0/0.1.18.73.0.0.1
/dev/dsk/c37t0d1
1/0/14/0/0.1.18.73.0.0.1
/dev/dsk/c33t0d1
1/0/14/0/0.1.19.75.0.0.1
Identification of devices in a multiple path I/O configuration can be challenging. The I/O stack
(driver) identifies devices using unique LUN IDs. Often this is a WWID value.
By identifying a device using the unique LUN ID, any of its hardware paths could be used to access
it, and agile addressing is supported.
The unique LUN ID might be difficult for a user to associate with a specific physical or logical
device. For example, often the device WWID is on a device label (e.g. on a sticker) or available
via storage management software used to set up a virtual LUN – those values are difficult to
remember and type correctly. It might be easier to select a device using one of its hardware paths.
72 Managing I/O for Installation and Recovery