Which new technologies are worth it?


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InfiniBand Server I/O

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Virtual pipes allow multiple fabrics to coexist on a single topology.

Lower SAN hardware costs. There are two flawed premises with this value proposition. The first is that current GigE and Ethernet product pricing will translate into lower iSCSI product pricing. The second is that FC pricing is high and will remain high. Both are incorrect. The iSCSI interfaces will require additional silicon to manage TCP/IP offload engines (TOEs), otherwise most of the CPU cycles will be utilized to read and write to disk instead of processing applications. This additional silicon increases costs, but FC costs have declined significantly. The price differential for optical interface adapters has become nominal, and there are even FC chips being put on the server motherboards for prices lower than iSCSI NICs. Even switch pricing has gotten fairly close. Category 5 is where iSCSI still has an advantage, since FC has no copper interface for 2Gb/s. When GigE and FC technology go to 10Gb/s, neither will have a copper interface. The value proposition accuracy: low.

Faster SAN deployments. The underlying premise is that the primary SAN deployment difficulty is FC complexity. The reality is the majority of that difficulty comes from making SAN-attached storage shareable. Ethernet and iSCSI do nothing to alleviate that complexity - Ethernet and iSCSI are less convoluted in how it's accomplished. The value proposition accuracy: medium.

Lower cost and simpler SAN management. The number of TCP/IP and Ethernet workers are greater than FC workers. It's likely that iSCSI and Ethernet SANs using current known management systems with extensions would be more intuitive to most IT organizations than FC SAN management systems. Even though most of the FC SAN management systems have borrowed heavily from common TCP and Ethernet management systems, they're still different. The value proposition accuracy: medium.

Elimination of interoperability issues. Today, FC interoperability issues are vendor-specific. The issue is essentially limited to FC switches and specific feature functionality, i.e., there's standard interoperability today and each vendor has value added extensions that only work with their equipment. The value proposition accuracy: low.

Elimination of multiple fabric infrastructures for client server and block storage. A total commitment to iSCSI on Ethernet for SANs would eliminate FC as a fabric to manage, providing a common technology for client server and storage networks. It wouldn't necessarily eliminate multiple fabrics - the characteristics of block SANs are different from client server, and usually require their own fabric. The only place iSCSI will have a significant impact on fabric consolidation is network-attached storage (NAS). Adding iSCSI to NAS means the file storage system can now run block storage on the same device. It not only consolidates storage fabrics, it consolidates storage devices. The value proposition accuracy: medium.

Elimination of distance boundaries for SANs. The only application driving SANs over distances larger than a campus is business continuity. Specific business continuity applications include disk-to-disk replication, disk mirroring and backup to tape or tape vaulting. FC manages this with technologies such as FCIP or iFCP (Fibre Channel frames tagged with an IP address). There's no significant advantage for iSCSI with these applications. The value proposition accuracy: low.

Equal or better performance than FC SANs. This claim was partially true when FC was at 1Gb/s. Now that nearly 100% of FC implementations are 2Gb/s, there's no truth in the claim. The other issue is the importance of low latency in SANs. GigE switches typically have multiple orders of magnitude greater latency than FC. The value proposition accuracy: low.

iSCSI provides some real capital and operating cost benefits for NAS/SAN combinations, and makes sense for organizations that don't need the performance of FC or don't want to go outside their comfort zone of Ethernet. However, it appears to have limited value for data centers.

This was first published in October 2002

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