User`s guide

Controller LUNs and SCSI host LUNs may represent the same structure,

but only if the user conﬁgures (up to) eight controller devices in a one-to-

one unit relationship with the host. This situation rarely occurs under

normal operation.

Host Port Target LUN Addressing (HSZ Array Controllers)

Note

Non-SCSI hosts (CI, DSSI), though they access virtual devices, do not use

a PTL addressing scheme. Any unit seen by these hosts is simply called a

host logical unit (not a LUN).

Host addressing is the process by which a SCSI host selects a logical unit made

up of physical devices connected to an HSZ array controller. The process takes

place in four steps:

1. The adapter selection—The host selects the adapter with one (or more)

SCSI–2 busses.

2. The port selection—The host selects the SCSI–2 bus that has the HSZ

array controller connected to it (for adapters with two or more SCSI–2 bus

interfaces).

3. The target selection—The host selects one of the controller’s SCSI IDs (that

is, the targets) on that port (bus).

4. The LUN selection—The host addresses the controller with the LUN of the

desired host logical unit. The controller translates the LUN into the physical

device addresses required to allow the host access to the virtual device.

1.6 HSJ Array Controller Dual Data Link

The HSJ array controllers fully support dual data link (DDL) operations. That

is, they can have operations in progress simultaneously on both CI paths. Either

receive/receive, receive/transmit, or transmit/transmit operations can be active

at the same time. The only restriction on a DDL operation is that simultaneous

transmit and simultaneous receive operations cannot be active on the same

virtual circuit. The packets that are simultaneously active can be to any two

separate CI nodes, or a transmit and a receive operation can be active to the

same node if it also supports DDL operation. Each CI path (Path A and Path B)

runs in half duplex, that is, it can either be transmitting or receiving, but not

both at the same time.

1.7 HS Array Controller Features

The following text, as well as Table 1–1, provides a summary of the features of

HS array controllers.

Remote system management is performed through the use of the following:

• DUP protocol for CI pass-through from the host to the controller’s CLI. The

HSJ and HSD30 array controllers support DUP connections.

1–12 Introduction to HS Array Controllers