Explain IP Storage standard.
1 Answer

The protocols available for transmitting storage data traffic over TCP/IP are as follows:

  • iSCSI

  • iFCP: Internet FCP

  • FCIP: FC over IP

These are IP-based storage protocols known as IP storage. These standards transmit SCSI over IP and in practice over Ethernet.

iSCSI transmit the SCSI protocol data over TCP/IP. In iSCSI, an SCSI cable is replaced by TCP/IP/Ethernet connection. iSCSI is installed in the OS as a device driver. Thus, it realizes an SCSI protocol and maps the SCSI daisy chain onto a TCP/IP network.

Traditional Ethernet network cards require the installation of a separate iSCSI device driver to implement the protocol in software to the cost of the server CPU to be used on servers. iSCSI is also implemented in hardware by using iSCSI HBAs to realise the iSCSI/TCP/IP-Ethernet protocol stack.

Just like TCP/IP offload engines (TOE), iSCSI HBAs handles a major part of iSCSI/TCP/IP/Ethernet protocol stack on the network and relieves the load on server CPU. Therefore, for higher performance requirement, iSCSI HBAs can be used and for low or average performance requirements, conventional, less expensive Ethernet cards are sufficient.

iFCP realises mapping of FC FCP on TCP/IP. The purpose is to reduce the investment in setting up an infrastructure with several FC devices that are already in place. iFCP merely replace the FC network infrastructure by an IP/Ethernet network infrastructure by an IP/Ethernet network infrastructure.

For the realisation of iFCP, FC F-Port or an FL-Port needs to provide on LAN switches. FC FCP-to-iFCP gateways are also being used. The difference between Metro FCP (mFCP) and iFCP is that mFCP is realised on UDP/IP and not on TCP/IP. Therefore, the performance of mFCP is dependent on the reliability of the underlying network connection. The error correction mechanisms in the application protocol are responsible to ensure that no data is lost. Therefore, it is desirable that it should have low-error networks such as LANs.

FCIP was designed to remove the distance limitations of FC. Organisation need longer distances to be spanned, say for backup and disaster recovery (DR) purpose. The production site and the DR and backup site have to be present in distant locations to prevent data loss in the event of large-scale catastrophes. The conventional way of doing this is taking the backup using tapes or sending through courier or using expensive and difficult means to manage WAN techniques.

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