Serial Attached SCSI technologies and architectures, 4th edition

requires half as many IO modules and expanders as other redundant storage configurations, so it is

economical.

Both SAS and SATA drives support dual-path configurations. Dual-path implementations cost less than

dual-domain SAS implementations but do not provide the full redundancy of a dual-domain SAS

solution.

Figure 7: A dual-path configuration for cascaded JBODs

Dual-domain SAS

Dual-domain SAS uses an open port on an HP Smart Array controller that can support dual-domain

SAS. The second port on the Smart Array controller generates a unique identifier and can support its

own domain. To take advantage of multiple domains, SCSI devices must be dual-ported and

connected to pathways in both domains. SAS drives can meet that requirement.

Dual-domain SAS implementations can tolerate failure of a host bus adapter (HBA), external cable, or

expander. They can also survive failure in a spanned disk (JBOD) environment or in RAID

environments. Dual-domain SAS solutions offer higher reliability, performance, and data availability

than SATA solutions.

Dual-domain SAS to JBOD

Figure 8 shows an example of a single controller capable of dual-domain support. The dual-domain

SAS configuration can tolerate simultaneous single port failure in a dual-port, dual-domain capable

controller, external cable failure, and expander failure. In the figure, the ―4\ ― notation indicates a 4-lane

bundled path. There are 4 wires per lane, or 16 total wires in a 4x cable.

Server

Disk drive

JBOD

Disk drive

JBOD

Disk drive

JBOD

Controller

IO Module

Expander

IO Module

Expander

IO Module

Expander