Connecting ISCSI SANs over a distance
The broad adoption of SoIP technologies, such as iSCSI, has further enhanced this connectivity. A storage manager uses existing network hardware and tools to create an Ethernet storage fabric that can easily transfer iSCSI SAN data across TCP/IP-based networks, including the Internet.
Let's look at the basic schemes used to connect SANs over a distance.
Even for a corporation with a substantial investment in Fibre Channel (FC) infrastructure, iSCSI provides economical SAN connectivity for workgroups and remote offices. Large companies are using iSCSI to connect many more servers to the SAN than they could otherwise afford using FC alone. FC and iSCSI SANs are typically tied together so that each SAN can access the other, but it's necessary for a storage router to convert between the two protocols. One example is the SANbox 6140 Intelligent Storage Router from QLogic Corp., which provides FC and Ethernet ports so that both SAN fabrics can be connected together.
Such local interconnections do not involve a WAN, but the practice is so common that it's worth mentioning here to put other WAN-based connections into perspective.
Two FC SANs can be conneced across an IP network using FCIP. This is a tunneling protocol that takes the FCP packets containing SCSI (not iSCSI) commands and encapsulates them within TCP/IP packets that are then exchanged over an Ethernet network, such as the Internet.
FCIP requires the use of a dedicated storage router, such as the Model 735 FCIP Storage Router from Emulex Corp. This type of device is located at each site, connecting the Fibre Channel fabric at each end to an Ethernet LAN and performing all the encapsulation functions in hardware at full T3 line speed. No special host bus adapters (HBAs) or other equipment should be needed to accomplish FCIP connections between SANs. FCIP management is typically handled by the storage administrator.
iFCP is a variation on FCIP that ports FCP directly to IP. There is no encapsulation because iFCP converts FCP packet addresses to corresponding IP addresses for transmission over the IP network or WAN. The iFCP packet is then reconverted back to FCP on the far end. However, iFCP is less popular today than FCIP.
As with local and FCIP connections, iFCP requires a dedicated storage router that supports the iFCP protocol, such as the M1620 from Brocade Communications Systems Inc. One device is needed at each end of the connection to interface the FC fabric to an IP network and perform the FC-to-IP translation in real time. Another distinction: FCIP management is handled by the storage administrator and iFCP management handled by the network administrator.
Storage managers considering a storage router should evaluate its compatibility with existing storage platforms. For example, Brocade claims that its storage routers are qualified with all major storage platforms including EMC Corp., Engenio Information Technologies Inc., Hitachi Data Systems (HDS), Hewlett-Packard, IBM, Sun-StorageTek and XIOtech Corp. Lab testing will determine the level of compatibility.
Also consider the benefits of data optimization functions available in the storage router. For example, the SANbox 6140 supports Ethernet jumbo frames that can increase the standard 1,500 byte packet to 16,000 bytes. By increasing the data payload in each packet, there are fewer handshakes to deal with, reducing latency and increasing the effective bandwidth. However, not all devices support jumbo frames properly. Testing will identify potential configuration problems early on.
04 Feb 2008