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How to pick the right protocol for your SAN

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Last month, we discussed transport issues for remote disaster sites (See "Linking SANs for disaster recovery, Part 1"). Once you have decided on the transport's physical infrastructure, deciding on the appropriate protocol to pump data to the other

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side will be your next major decision.

If your requirements dictate and your budget allows for dense wavelength division multiplexing (DWDM), then you probably want to maintain native Fibre Channel (FC) communication between the initiator and target storage area network (SAN) device. If you've chosen TCP as your WAN transport mechanism, you have three choices for protocols:

  • Fibre Channel over IP (FCIP)
  • Internet Fibre Channel protocol (iFCP)
  • Internet SCSI (iSCSI)
As to which one you choose, it depends on the design of your current FC SAN (if you have one), as well as the time it will take for iSCSI to prove itself with enterprise applications.

How iFCP works
iFCP gateways can connect multiple SANs to multiple SANs through an IP cloud. Each sending SAN switch sends packets (1) to the iFCP gateway, which encapsulates them (2) and tracks both the IP and FC addresses of all the attached nodes. The receiving gateway strips off the IP packet (3) and sends the FC payload to the appropriate SAN (4) on the receiving side.

How FCIP works
FCIP creates a direct connection between SANs. The FC packet (1) is sent to the FCIP bridge, where it is encapsulated within an IP packet (2) and sent over an IP link to the receiving bridge, which strips off the IP header (3) and sends it to the receiving FC switch (4).

This was first published in October 2003

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