intro.7 (2010 09)

intro(7) intro(7)
by period (.) characters. All the elements are represented in decimal. This is the format printed by
default by the ioscan command for most devices. An example of a legacy hardware path is
0/0/2/0.1.7.0
.
The lunpath hardware path is used for mass storage devices, also known as logical units (LUNs). It is
identical in format to a legacy hardware path, up to the HBA. Beneath the HBA, additional elements are
printed in hexadecimal. The leading elements representing a transport-dependent target address, and
the final element is a LUN address, which is a 64-bit representation of the LUN identifier reported by the
target. This format is printed by the
ioscan command when the -N option is specified. The string
0/2/1/0.0x50001fe1500170ac.0x4017000000000000
is an example of a lunpath hardware
path.
Note that the address elements beneath the HBA may not correspond to physical hardware addresses;
instead, the lunpath hardware path should be considered a handle , not a physical path to the device.
The LUN hardware path is a virtualized path that can represent multiple hardware paths to a single
mass storage device. Instead of a series of bus-nexus addresses leading to the HBA, there is a virtual
bus-nexus (known as the virtual root node ) with an address of 64000. Addressing beneath that virtual
root node consists of a virtual bus address and a virtual LUN identifier, delimited by slash (
/) characters.
The string
64000/0xfa00/0x22
is an example of a LUN hardware path.
As a virtualized path, the LUN hardware path is only a handle to the LUN, and does not represent the
LUN’s physical location; rather, it is linked to the LUN’s World Wide Identifier (WWID). Thus, it
remains the same if new physical paths to the device are added, if existing physical paths are removed, or
if any of the physical paths changes. This LUN binding persists across reboots, but it is not guaranteed
to persist across installations — that is, reinstalling a system or installing an identically configured sys-
tem may create a different set of LUN hardware paths.
Device File Types (Mass Storage Devices)
Mass storage devices, such as disk devices and tape devices, have two types of device files, persistent dev-
ice special files and legacy device special files. Both can be used to access the mass storage device
independently, and can coexist on the same system.
A persistent device special file is associated with a LUN hardware path, and thus transparently supports
agile addressing and multipathing. In other words, a persistent device special file is unchanged if the
LUN is moved from one HBA to another, moved from one switch/hub port to another, presented via a
different target port to the host, or configured with multiple hardware paths. Like the LUN hardware
path, the binding of device special file to device persists across reboots, but is not guaranteed to persist
across installations. The device special file name follows the standard naming convention above, and the
minor number contains no hardware path information.
A legacy device special file is locked to a particular physical hardware path, and does not support agile
addressing. Such a device special file contains hardware path information such as SCSI bus, target, and
LUN in the device file name and minor number. Specifically, the class and instance portions of the device
special file name indicate hardware path information and are in the format
c#t
#d# as follows:
c# The instance number assigned by the operating system to the interface card, in decimal.
It is a decimal number with a range of 0 to 255. There is no direct correlation between
instance number and physical slot number.
t# The target address on a remote bus (for example, SCSI address). It is a decimal number
with a typical range of 0 to 15.
d# The device unit number at the target address (for example, the LUN in a SCSI device). It
is a decimal number with a typical range of 0 to 7.
Note that the legacy naming convention supports a maximum of 256 external buses and a maximum of
32768 LUNs. Systems with mass storage devices beyond those limits will be unable to address them
using legacy naming conventions.
Legacy device special files are deprecated, and their support will be removed in a future release of HP-
UX.
Viewing Mass Storage
With the advent of persistent and legacy device special files, commands dealing with mass storage can
choose between two views of the I/O system. A command presenting the legacy view uses legacy device
special files and legacy hardware paths. The agile view uses persistent device special files, lunpath
hardware paths, and LUN hardware paths.
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