HP Cisco Nexus 5000 Cisco MDS 9000 Family CLI Configuration Guide - Release 4. - Page 530

About SDV Chapter 21 SAN Device Virtualization Send documentation comments to [email protected] Figure 21-1 Target Virtualization Server Virtual target Primary target Traffic from server Secondary target 183017 Figure 21-2 Initiator Virtualization Primary initiator Virtual initiator Secondary initiator Traffic from server 183018 Note While most of the examples in this chapter describe target virtualization, the initiator virtualization functions similarly. Typically, today's deployments for handling device failures are designed for high availability (HA), with redundancy being a key part of this design. Consider the situation where a target is designed to be redundant. Two arrays are deployed-a primary and secondary in this situation. Enterprises often use some type of consistency technology (such as EMF SRDF) between the primary and secondary arrays to ensure that the secondary is a mirrored copy of the production LUN. However, if the primary array fails, it must be replaced by the secondary because all I/O must occur on the secondary array. Problems can occur because the time required to bring the secondary array up and have it working often takes longer than most can afford (Figure 21-3 illustrates this dilemma). Figure 21-3 Typical Deployment for Handling Device Failures Before SDV Servers SAN Primary Device I/O - Normal I/O - After primary failure Secondary Device Asychronous Replication 182097 21-2 Cisco MDS 9000 Family CLI Configuration Guide OL-18084-01, Cisco MDS NX-OS Release 4.x