Maximizing FC SAN investments with iSCSI - Storage Networking

Businesses have made significant investments in their Fibre Channel storage area networks. The challenge is to leverage the FC SAN so that these investments in capital equipment, staff and infrastructure deliver ever-increasing value to the business. The majority of the FC SAN investments are not raw disk capacity, but infrastructure costs such as: disaster recovery mechanisms, high availability systems, backup, monitoring, security and resource allocation tools. Equipment investments include: FC switches, routers, storage enclosures, host HBAs and backup devices. Soft dollars include management, staff, software agents, upgrades, maintenance and facility.

Increased FC SAN ROI and value comes by increasing productivity, which means adding more users, encompassing a greater number of application servers and expanding the total amount of hosted data. Many businesses have been reluctant to put more servers and clients on the SAN. High per-server attachment costs and management complexity are major factors limiting the expansion of FC SANs. This has created a dilemma for many IT managers who want to fully utilize their FC SANs but find it difficult to justify the addition of more servers or clients.
A new standard for expanding SANs was required that would allow businesses to realize the full benefits of their FC SAN investments by greatly reducing the costs associated with connecting servers to the FC SAN. The IETF/IEEE committee and industry leaders worked together to create the new iSCSI storage protocol. iSCSI solved many of the problems causing the slow expansion of FC SANs. This new storage protocol resides on top of TCP/IP over Ethernet. Unlike Fibre Channel, iSCSI uses Ethernet and does not require special equipment or cabling. It can use common Ethernet NICs (network interface cards), switches, hubs and cabling.

The Benefits of iSCSI are Clear for Expanding FC SANs:

* Based on IETF standards to insure interoperability

* iSCSI SAN connectivity costs are 1/2 to 1/5 that of FC

* Uses existing Ethernet cabling and existing network elements

* Uses common TCP/IP for global connectivity

* Leverages the existing expertise of IT professionals

* Is being quickly adopted by system, storage, and network vendors

* Provides the same reliability as FC

Leverages IP Security (e.g. SRP, CHAP, and IPSEC) Table 2 shows relative costs for connecting application servers using FC vs. connecting the same servers or clients to an iSCSI / Ethernet Storage Network.

iSCSI to FC Gateways

Using an iSCSI gateway to the FC SAN can increase the number of application servers and clients storing their data within the FC SAN infrastructure. A gateway resides at the edge of the FC SAN, between the FC SAN and Ethernet network. Hosts traffic data using iSCSI between themselves and the gateway over a common Ethernet network. The gateway converts the traffic to FC and routes it to the designated storage LUNs within the FC SAN. Gateways are equipped with 2 to 4 FC Ports for connecting to the SAN and an equal number of Gb Ethernet ports for connecting to the Ethernet network. New hosts connected to the same Ethernet network will be able to access the FC SAN through the gateway.

The SAN infrastructure does not need to change when attaching the gateway. The gateway is attached via its FC ports that resemble host HBAs. The FC SAN administrator simply needs to provide access to storage LUNs for the gateway, just as it would provide storage resources to a basic server. The gateway will discover and log on to the storage resources and read and write to them in the same manner as an FC server. Figure 1 shows a typical high availability configuration with clustered gateways being used to connect iSCSI enabled servers to the FC SAN.

Volume Management Within the Gateway

One of the major issues in extending a SAN using a gateway is the task of managing the storage resources for a few to hundreds of new hosts and clients. The number of hosts and clients connected over iSCSI can become a fairly high number and be distributed over a large geographic area or even into another country. Traditional methods for volume management are far too expensive, complex and maintenance intensive to support this type of infrastructure.