HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

is the default load balancing algorithm for serial devices (for example
tape drives).
preferred_path
The I/O path set in the preferred_path attribute is preferably used for I/O
transfer. If this I/O path is not available or if the preferred_path attribute
was not set, any other path is selected for I/O transfer. This policy is useful
for certain disk arrays, which may exhibit some performance degradation
if I/Os are transferred via several I/O paths to a LUN simultaneously.
pref_tport
This load balancing policy selects LUN paths from a preferred list unless
none are available (or defined), in which case other LUN paths are selected.
wt_round_robin
This load balancing policy selects an I/O path based on a weighted round
robin algorithm
Use the scsimgr command to specify which of the previous policies should be used for a given
device.
NOTE: Not every device supports every load balancing policy. The type of device determines
which of the previous policies you can use. For details see the following manpages:
scsimgr(1M)
scsimgr_eschgr(7)
scsimgr_esdisk(7)
scsimgr_estape(7)
HP-UX can also automatically re-balance the loads on remaining data paths to a LUN should
one or more of those paths fail.
NOTE: Use the scsimgr command (see scsimgr(1M) for details) to set the load balancing
algorithm. An algorithm choice can be set individually for each LUN, or for all LUNs on the
server. Also, the choice can be permanently set (value retained across reboots), or temporarily
set (until the next reboot).
Device Special File Directories (and Name Formats)
Device Special Files are located in the /dev directory and many are organized in a series of
sub-directories within /dev. Two of these directories contain the persistent device special files
defining the physical disk drives on a server:
/dev/disk
Contains persistent device special files for block mode access to physical disk
devices on a server.
/dev/rdisk
Contains persistent device special files for character mode access to physical disk
devices on a server.
Within the previous directories, files have names in the format diskN (where N is the instance
number of the disk).
Examples:
/dev/disk/disk15
/dev/rdisk/disk7
An optional part of a device file name for a disk can be appended to represent disk partition
numbers. By convention, in the absence of this optional part of the device file name the name
represents an entire disk. This optional part expands the format of the name to be diskN_p#
(where p# represents the partition number, tape density, or other information).
Examples:
/dev/disk/disk15_p3
/dev/rdisk/disk7_p1
Storage on HP-UX 55