HP-UX Reference (11i v3 07/02) - 7 Device (Special) Files, 9 General Information, Index (vol 10)
intro(7) intro(7)
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 system 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 device
special files and legacy device special files. Both can be used to access the mass storage device indepen-
dently, 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 instal-
lations. 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.
Depending on the command, both views may be presented, or the choice of view may be controlled by a
command option or an environment variable. For example, the ioscan command shows the legacy view
by default, and switches to the agile view if the -N option is specified.
EXAMPLES
Example 1
The following is an example of a persistent device special file name:
/dev/disk/disk3
where disk indicates block disk access and disk3 indicates device class disk and instance number 3. The
absence of p# indicates access to the entire disk; see disk(7) for details.
Example 2
The following is an example of a legacy disk device special file name:
/dev/dsk/c0t6d0s2
18 Hewlett-Packard Company − 2 − HP-UX 11i Version 3: February 2007