7.4 iSCSI Storage Devices

The first iSCSI storage target was the IBM 200i disk array. This was a medium- to low-performance storage target that was more of a technology showpiece than a serious contender for market share. Because of its moderate performance and lack of customer appeal, IBM eventually withdrew active marketing of the 200i, causing much gossip in the trade press at the time.

It is unfortunate that the first iSCSI storage target was performance-challenged. As with other poorly performing early market products, the lack of rigorous engineering fostered the belief that iSCSI was unsuitable for mainstream SAN applications. Some vendors themselves have encouraged this impression, marketing their iSCSI solutions for low-end applications such as backup of laptop PCs.

In fact, there is nothing in the iSCSI protocol or product implementation that limits it to the low end of the market. Like FCP, iSCSI is simply a serial encapsulation of SCSI. With TCP offload on end systems, iSCSI can deliver high performance with minimal processor overhead. For manufacturers of storage arrays and tape subsystems, then, iSCSI is simply one more interface that serves as a front end to their storage target.

iSCSI-attached storage arrays and tape offer the same advantages and flexibility as iSCSI adapters. Whereas Fibre Channel cut the umbilical cord of parallel SCSI cabling, iSCSI cuts the tether of Fibre Channel cabling. With 1Gbps or 10Gbps Ethernet interfaces on the storage target, it can be deployed anywhere within the IP routed network, as shown in Figure 7-4.

Figure 7-4. iSCSI targets can be deployed anywhere within the IP routed network

Although engineering an iSCSI interface for a RAID or tape subsystem is fairly straightforward, the one storage device that cannot be easily converted to iSCSI is the JBOD. An iSCSI JBOD would require iSCSI interfaces on individual disk drives. At the moment there is no compelling reason for disk drive manufacturers to support iSCSI in addition to SCSI and Fibre Channel. JBOD support in a pristine iSCSI environment would therefore require an iSCSI-to-SCSI bridge or an iSCSI-to-Fibre Channel gateway.

In terms of storage functionality, the substitution of an iSCSI interface for a Fibre Channel interface does not alter the basic requirements of storage configuration or management. You still need a means to zone authorized resources, manage LUN visibility through LUN masking, provide dual or multiple pathing, support failover, and so on. In addition, with the continued development of array-based storage virtualization, this new intelligence will start appearing behind an IP-based interface. iSCSI enables storage to be more ubiquitous in the network; virtualization will make it much simpler to manage.