Overview: The Next Generation Mass Storage Stack (September 2009)

Feature HP-UX 11i v3 HP-UX 11i v2
Number of I/O busses no limit 256
Number of LUNs supported 16384
(architectural limit of 16 M)
8192 active
LUN size > 2 TB (subject to driver support) 2 TB
Number of I/O paths to a single LUN 32 8
File system size supported 32 TB at initial release
(subject to volume manager support)
(architectural limit of 8 EB)
32 TB
In addition, the mass storage stack has been enhanced to take advantage of large multi-CPU server configurations
for greater parallelism. Adding more mass storage to a server does not appreciably slow down the boot process
or the ioscan command.
Impact
The increased limits do not affect the usage of any commands or libraries. Some command output fields can
appear wider due to larger numbers.
One significant change is in hardware paths and DSFs. The increased number of I/O busses and LUNs makes
encoding path information in the DSF minor number impractical, so the I/O subsystem has introduced a new
naming convention and minor number convention for mass storage devices. If you have any existing DSFs, they
are completely backward compatible. However, you cannot use existing DSFs to address more than 256 I/O
busses or 32768 LUNs. In HP-UX 11i v3, you can use new DSFs that enable the larger I/O configurations,
transparent multi-pathing, and agile addressing.
For additional information on scalability and mass storage limits in HP-UX 11i v3, see the HP-UX 11i v3 Mass
Storage I/O Scalability white paper in For more
information.
Agile Addressing
The most visible change to the mass storage stack in HP-UX 11i v3 is the addition of agile addressing, also
known as persistent LUN binding.
Background
Historically, DSFs for mass storage devices had their hardware path, or lunpath, encoded in both their name
and their minor number. For example, the DSF /dev/dsk/c3t15d0 is at SCSI controller instance 3, SCSI target
15, and SCSI LUN 0. This legacy style of DSF has three significant shortcomings:
• If any mass storage had multiple lunpaths, there were multiple DSFs, one for each lunpath. All disk
management products had to be aware of multiple paths, with each product generating its own, often
conflicting, solution.
• If the path to a disk changed, the names of its associated DSFs had to change as well, requiring
applications and volume groups to be reconfigured. In SAN environments, an HBA port change, switch
port change, or controller port change can trigger such hardware path changes.
• The size of the I/O configuration was limited by the format of the DSF minor number and naming
convention. With reserved bits for the card instance, target, and LUN, only 256 controllers, 16 targets per
controller, and 8 LUNs per target were allowed. Interface drivers that supported the larger addressing
model of SCSI-3 devices had to create virtual controllers, virtual targets, and virtual LUNs.
In HP-UX 11i v3, you can create persistent DSFs; that is, you can create a single DSF for each unique LUN in
the server, no matter how many lunpaths the LUN has or if any of those lunpaths change. With this persistent
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