Monday, May 22, 2006

iSCSI

What is iSCSI?

iSCSI (Internet SCSI) is a protocol which is used to link multiple storage devices like SANs, drive arrays or tape devices over regular IP based networks or the internet. It does this by encapsulating the data and SCSI commands between multiple devices.
iSCSI is supported over almost all platforms like Microsoft, Linux, Sun, IBM etc. iSCSI works at the transport layer of the OSI model.

Is iSCSI same as SAN?

Not exactly. In case of SANs, iSCSI is better aligned with IP SAN. IP SAN is an external storage box which can mount data from multiple servers on multiple volumes. So in general, if a company is not very sure about the growth of data in the coming times, it becomes very difficult for them to right size the servers in terms of storage. An IP SAN gives them the flexibility to invest once and mix and match storage requirements on any server as per requirement, without having to resize the server or move to a bigger box.
Some people believe that an IP SAN using iSCSI cannot deliver the same performance as a fiber based SAN. This is not quite true since iSCSI uses a technology called as TCP Offload Engine (TOE) to reduce the overhead of adding TCP/IP data to the data packet.
iSCSI is a completely different technology and should not be confused with a NAS device.

What is different in iSCSI than other related technologies?

1. iSCSI, a block based storage protocol, is superior in speed (up to 10 times faster) to NFS, CIFS file-based protocols. Therefore, iSCSI can be used with any application including databases.

2. The ease of use of iSCSI and the vast support from different OS’s enable the easy transfer of complete volumes from one host to the other as needed, without investing in additional infrastructure or complicated management schemes.

3. iSCSI delivers everything you can get from Fiber Channel protocol, at 1/2 to 1/5 the price, by deploying highly managed IP SAN infrastructures without building dedicated Fibre Channel infrastructures.

4. iSCSI protocol can deliver block based storage over any kind of IP network. So it can be used for advanced storage applications such as Disaster Recovery.

How to setup iSCSI?

iSCSI needs an iSCSI initiator. Many operating systems provide them built-in with their product. There are also hardware HBAs available for this. As you would notice in this article, the setup or operation of iSCSI does not requires the use of fiber channels at any point.

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