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If a mission-critical enterprise environment like that of Fortis' is satisfied with iSCSI, what's keeping it out of enterprise data centers? "Companies that have a large and underutilized Fibre Channel infrastructure are less interested in iSCSI," says Robert L. Stevenson, managing director, TheInfoPro's storage sector. "But when that existing investment in FC isn't there, or if the utilization of FC ports gets high, interest in alternatives quickly arises." This is a key point: Many firms have built out massive FC SANs with less-than-total utilization. If excess capacity is available, there's little need to invest in a new array in general or an unfamiliar protocol in particular; iSCSI tends to be deployed in areas that haven't been served by any networked storage.
Bridging the gap
When iSCSI is deployed in an enterprise data center, it's often hooked into the FC SAN. Rather than buying end-to-end, iSCSI-only solutions with integrated disk drives, enterprise users are focused on leveraging their existing infrastructure. Although native integrated iSCSI adapters are available for most new arrays, older arrays might not have this capability, so companies turn to iSCSI gateways and bridging technologies. These may take the form of iSCSI routers like those produced by Hewlett-Packard (HP) Co. and Sanrad Inc., mimicking the popular "NAS heads" that provide file services in similar situations, or that could be integrated with FC network gear from Brocade
While selecting an iSCSI product has more to do with the practical considerations of compatibility with existing equipment, there are technical factors to consider. Integrated iSCSI controllers are simpler to configure and manage than an external controller. Integrated controllers normally use the same configuration software and the same commands as FC adapters, but offer little in the way of advanced features. Moving the iSCSI controller outside the array increases the complexity of the overall solution, but allows storage from multiple arrays to be combined and presented to iSCSI-attached servers more flexibly, even if the arrays are of different types. Dedicated iSCSI routers generally offer the most functionality, but you must learn a new management interface. These devices often integrate heterogeneous replication features and other storage virtualization techniques that can prove extremely valuable.
Although a smaller firm may be reluctant to front an expensive and complicated enterprise array with "low-cost" iSCSI, enterprise users see no such contradiction. On the contrary, they value the simplicity and flexibility of standardizing on a single disk platform regardless of the protocol used by attached servers. By having just one type of disk, they can smooth out their storage capacity procurement, averaging out the unpredictability of purchases with a larger set of users. If unexpected demand emerges from one app or another, disk space can be easily reallocated among FC, iSCSI and NAS.
This was first published in July 2007