HP-UX iSCSI Software Initiator Support Guide, HP-UX 11i v1 and 11i v2, July 2005

Chapter 2
HP-UX iSCSI Software Initiator Product Overview
Targets
26
Static Discovery
Static discovery requires the system administrator to identify all iSCSI discovery targets that will be
accessible to an HP-UX host before an ioscan is executed. The configuration is done using the iscsiutil
tool (see “The iscsiutil tool” on page 55, for details). Targets are defined using either their IP addresses or
their DNS host names, combined with:
— the TCP port number on the iSCSI target used for iSCSI access
— the target portal group tag
The iSCSI target information that is entered through the iscsiutil tool will be maintained in a persistent
area of storage called the kernel registry. It is only necessary to enter the target data once, because the kernel
registry data will persist across reboots and upgrades.
When an ioscan is initiated, the iSCSI Software Initiator performs a probe by obtaining the target data from
the kernel registry and then attempting to establish a session with the iSCSI discovery target. If an iSCSI
session is established, a successful discovery login with the iSCSI discovery target is implied. A successful
discovery login will result in operational targets (reported behind a discovery target) being registered into the
kernel registry. A successful discovery session will be closed when the probe is complete.
An iSCSI normal session is established to each operational target registered in the kernel registry. An iSCSI
normal session is identified by a session instance identifier. Once the normal session has been successfully
established, the HP-UX iSCSI Software Initiator will determine the number of LUNs behind the target. Any
LUNs found are used to define SCSI-2 virtual busses that will later be used for SCSI-2 target and LUN
probing by the SCSI Services layer.
An iSCSI session will be used to define one or more SCSI-2 virtual busses. The virtual busses are necessary
because iSCSI target storage is defined using SAM-2 (SCSI-3), but HP-UX supports SCSI-2.
SCSI-3 LUNs behind a target will typically be defined sequentially starting at LUN 0. Because the SCSI-2
implementation only permits 128 LUNs per bus, the bus mapping will define a virtual bus for each 128 LUN
grouping. Thus, if one or more LUNs exist in the range 0-127, then the iSCSI Software Initiator creates
virtual bus 0. If one or more LUNs exist in the range 128-255, then the iSCSI Software Initiator creates
virtual bus 1, etc. This process is repeated until all SCSI-3 LUNs on the iSCSI target are mapped to HP-UX
iSCSI virtual busses. Next, the HP-UX SCSI Services will probe the virtual SCSI-2 busses and define SCSI-2
virtual targets and LUNs.
NOTE Traditionally, HP-UX has used the ioscan tool to dynamically discover all possible targets and
LUNs accessible by a host. Dynamic discovery is only available for iSCSI targets that support
Service Location Protocol (SLP), provided SLP is available to the HP-UX host.
Service Location Protocol Based Dynamic Discovery
Service Location Protocol (SLP) is used for iSCSI dynamic discovery. The islpd daemon is a user space
daemon that implements the SLP User Agent (UA) and the interface to the iSCSI transport driver.
The HP-UX SLP components must be separately installed on the system. See Table 2-1, “SLP Server
Installation Information and Related Documents,” on page 27, for detailed information.
The Directory Agent (DA) can be on the same system, or on any other system in the same subnet. Targets
must be on the same subnet as the DA to be discovered by the DA. At least 1 DA must be present on the
subnet. Dynamic scanning based on SLP is triggered when the ioscan command is executed. The islpd
queries the DA(s) on the subnet for all of the iSCSI targets. Only targets that support SLP (and have been
configured to use SLP) will be registered with the DA. Each target address supplied by the SLP DA is entered
into the kernel registry as an operational target.