Serial Attached SCSI technologies and architectures, 4th edition

Figure 11: Dual-path configuration for cascaded JBODs

Zoning

Zoning breaks topologies into logical groups for better traffic management and security. Zoning uses

the unique ID number of each expander PHY to provide a secure method of managing SAS devices.

You can assign expander ports to zone groups. Any device attached to one of the ports becomes part

of that respective zone group.

By default, all devices within a zone group can interact with each other. The permission table in the

expander controls access between devices in different zone groups.

If you swap a device attached to an expander for another device, you can configure the expander to

set the zone group to 0 (no access). That allows you to implement a policy similar to an address-

resolved policy. For example, if a particular SAS device needs to have certain permissions, you can

move the device to a different expander in the fabric. Then you can reprogram the zone group at the

new location.

Logical grouping allows zoning access within and between controlled zone groups. A zoned portion

of a service delivery system (ZPSDS) consists of a group of zoning-enabled expanders that cooperate

to control access between PHYs.

The SAS-2 standard allows either 128 or 256 zone groups (numbered from 0 to 127 or 0 to 255).

Zone groups 0 through 7 are pre-defined, and administrators cannot change them. Devices in zone

group 0 can only access devices in zone group 1. Devices in zone group 1 have access to all zone

groups. For example, you can use zone group 0 to add a new (unassigned) device to a ZPSDS. The

new device is hidden from other devices until you assign access to it by changing its zone group. At

the same time, you can use zone group 1 for topology discovery and zone management because it

has access to all zone groups.

An end device does not need any special features to operate within a zoned SAS domain, so SAS

fabrics support both SAS and SATA end devices. The zoning expander controls whether an end

device in a zone can communicate with other end devices in the same domain. Figure 12 shows a

Server

Disk drive

JBOD

Disk drive

JBOD

Disk drive

JBOD

Controller

IO Module

Expander

IO Module

Expander

IO Module

Expander