HP-UX 11i v3 Mass Storage Device Naming

legacy naming
model / legacy
format
Device special file format convention used prior to HP-UX 11i v3. This
model is maintained in HP-UX 11i v3 for backward compatibility
purpose.
(legacy) DSF A path dependent device file, following the legacy naming model
conventions, wherein the DSF embeds the bus/target/lun/option for a
specific path to a mass storage device (Ex. /dev/dsk/c#t#d#).
SCSI class driver A HP-UX device driver which manages one or more specific classes of
mass storage devices. Ex : Disk Driver, Tape Driver, Changer Driver,
Pass-thru Driver.
Target Id Corresponds to the target port identifier as defined in SCSI transport
protocols
Introduction
HP-UX 11i v3 introduces a new agile addressing scheme for mass storage devices, with opaque
minor numbers, persistent device special files (DSFs), and new hardware path types and formats. The
addressing scheme used in previous HP-UX releases, will co-exist with this new scheme to ensure
backward compatibility and is referred to as legacy addressing. The legacy addressing will be
deprecated in a future HP-UX release.
In the legacy addressing scheme, each device path is represented by a minor number, a legacy DSF
and a legacy hardware path. The minor number directly encodes SCSI-2 addressing information
(SCSI bus, target address and logical unit number), and device options (disk partition number, tape
density, etc.). The legacy DSF name also embeds SCSI-2 addressing information. This has the
following limitations:
• A device with multiple paths is represented by several legacy device special files.
Applications and upper layer modules (File system, volume manager, etc.) have to use
independent methods such as writing meta data on the device to be able to determine that
different legacy DSFs correspond to the same device.
• Limited scalability: legacy limits of 256 SCSI bus instances, 16 target identifiers per bus
instance and 8 logical unit numbers per target identifier. The use of 15 bits to encode the
minor number limits the overall number of lunpaths to 32768.
• Dependency on the physical connection of the device. If for instance the device is connected
to the host through a different host-based adapter (HBA) or a different target port, the device
special file and the minor number may be affected requiring a re-configuration of
applications or upper layer modules such as volume managers and file systems.
The agile addressing scheme addresses each of these limitations:
• It defines a persistent device special file and a virtualized hardware path, which represent the
device independently of its paths. So a device with multiple paths is represented by a single
device special file.
• It increases the scalability by using 24 bit opaque minor numbers and storing the device
options separately. The binding between a minor number and certain device options is
maintained in a system registry.
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