HP-UX iSCSI Software Initiator Support Guide (Edition 7)

2.3.2 Device Discovery
The implementation of iSCSI on HP-UX uses a static discovery algorithm as the default means of
identifying iSCSI targets (devices). As an option, dynamic discovery of targets is available using
Service Location Protocol (SLP).
2.3.2.1 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 ioscanis executed. The configuration is done using the
iscsiutil tool (see “The iscsiutil tool” (page 28), 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 ioscanis 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. The successfully established
normal sessions are probed by scsi services to discover the SCSI-3 luns.
NOTE: Traditionally, HP-UX has used the ioscantool 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.
2.3.2.2 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: “SLP Server
Installation Information and Related Documents” (page 15), 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 ioscancommand
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.
14 HP-UX iSCSI Software Initiator Product Overview