Maximum LUN Configuration and Considerations for HP-UX

Abstract
Mass storage requirements have increased dramatically over the last few years. High-end HP-UX
customers now require many terabytes of storage and thousands of storage devices (LUNs) to be
accessible from a single HP-UX server. This paper highlights the increases in the maximum number of
LUNs supported with HP-UX servers and at component levels such as per-HBA (Host Bus Adapter). The
nature of these maximums is defined, along with recommendations or restrictions that apply when
operating at or near these maximums, and expectations for the future and what to do if you must
exceed supported levels.
Terms and Definitions
HBA Host Bus Adapter. A physical I/O interface that provides I/O processing
and connectivity between a system I/O bus such as PCI and a storage
device. Examples include parallel SCSI, Fibre Channel, and Serial Attached
SCSI.
LUN Logical Unit Number. The addressing identifier of a SCSI logical unit, but
also used to refer to the device or piece of storage, or even a hardware path
to the device. To distinguish between the actual device and a path to that
device, this paper uses the terms "LUN device" and “LUN path” respectively.
Dynamic Multi-pathing The ability to determine the various paths to a given LUN device at runtime
and to dynamically load-balance I/O operations across those paths.
Active LUN path A load-bearing path to a LUN device. The path is actually used for normal
I/O transfers. A dynamic multi-pathing module can use it to load-balance
I/O operations.
Open LUN path An "Active LUN path" or a path that is opened with only occasional I/O to
the LUN.
Visible LUN path An "Open LUN path" or a path that is typically not open but is visible to the
ioscan command.
Active LUN device A LUN device with at least one Active LUN path.
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