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The best way to expand a SAN

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Protocols
Growing a SAN cost-efficiently requires storage architects to look beyond FC. While iSCSI is being embraced by smaller companies as their primary SAN, it can be leveraged in FC SAN environments for less critical applications like disk-to-disk backup and departmental applications. With all major storage vendors supporting both FC and iSCSI, consideration of the iSCSI option should be part of any new SAN deployment and SAN expansion project. However, iSCSI's lower cost and complexity need to be weighed against its slightly lower performance and its spotty support in storage management applications today.

"We are seeing companies with existing FC SANs using iSCSI to connect midrange and workgroup servers for which FC can't be justified," says Rajeev Bhardwaj, senior manager of Cisco's storage business unit within the Data Center Business Unit. Multiprotocol support in directors, as well as dedicated iSCSI gateways and routers from companies like Brocade, Emulex and McData, enable enterprise customers to attach servers via iSCSI to their existing FC storage.

Bringing iSCSI into an FC SAN will definitely result in a somewhat more complex SAN that requires mastering the idiosyncrasies of two different SAN technologies that have their own unique requirements. "We have been evaluating iSCSI through an eight-port IP line card in our Cisco MDS 9509 directors," says Follstad at the University of Minnesota. "An ongoing LAN restructuring

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project and the lack of a Radius server infrastructure for CHAP [challenge handshake authentication protocol] authentication were some of the hurdles we had to overcome."

Storage managers trying to cut costs also need to decide how best to bring NAS into the SAN mix. The benefit of NAS for file access is its inherent ability to serve files in both CIFS and NFS file-system protocols, making files accessible to both Windows and Linux-/Unix-based systems. Most large storage vendors, including EMC, Hewlett-Packard Co., Hitachi Data Systems (HDS) and IBM Corp., have embraced NAS in the enterprise by offering midrange to large-scale systems as well as NAS-to-SAN gateways.

NAS gateways provide NAS head functionality for CIFS and NFS access to SAN storage. In other words, NAS gateways are NAS units that substitute a dedicated disk subsystem with storage from the SAN storage pool, consolidating NAS and SAN storage, and lowering both storage acquisition and maintenance costs. "By using two EMC Celerra NS704G NAS gateways, we are able to offer NFS file access by leveraging our current investment in Clariion and Symmetrix storage," says Follstad.

This was first published in July 2006

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