Tuesday, 1 May 2007

what the hell is i-SCSI ? -Ashwin


what the hell is i-SCSI ?

When i first heard this term two years back , i thought it is "Ice-SCSI", it sounded like that, and for no reason i felt it is something complicated technology and my assumption was quite natural and i guess every individual have certain assumption on the way technical term sounds, though my theory of assumption is ridiculous but let me tell you its not complicated.

Coming back to "What is I-SCSI" ? , let me try to explain in the less complicated manner.

I-stands for Internet and SCSI as you know stands for Small Computer System Interface. SCSI deals in "Blocks" and Internet deals in "Packet" i.e IP Packet. Here both SCSI and Ethernet technology work together to perform SCSI Data transfers over TCP/IP networks.

It basically allows the block storage SCSI commands to be carried by the standard TCP/IP protocols over the Ethernet wire.

Until recently, Ethernet was too slow to compare to the performance of direct attach storage. With the advent of 1 Gigabit and 10 Gigabit Ethernet, an Ethernet network is now fast enough to use for storage applications.

Technically, this is how it works:
Basically, iSCSI is composed of "initiators" and "targets" that will be used at both ends of the Ethernet wire. The iSCSI initiator connects the computer that initiates the request for data stored on the disk with the Ethernet wire. The iSCSI target connects the Ethernet wire with the storage device, whether it be an array of disks or perhaps a tape device. The initiator encapsulates the SCSI commands and data, so that they can be sent over TCP/IP; and, the target extracts the commands and data at the storage device end of the wire.

From end-user point of view, this is how it works:
When an end user or application sends a request for data, the operating system creates the appropriate SCSI commands, which then go through encapsulation and, in some circumstances, encryption. A packet header is added to the resulting IP packets, and the data is transmitted, typically over an Ethernet connection. When a packet is received, it is decrypted and disassembled, separating the SCSI commands and the data request. The SCSI commands are sent on to the SCSI controller, and from there to the storage device. Because iSCSI is bi-directional, the protocol can also be used to return data in response to the original request.

IBM is already shipping a native iSCSI IP storage system, the IBM TotalStorage IP Storage 200i. Analysts say other companies will speed products to market, once the IETF formalizes the standard. Since 2001 , other companies have also introduced ISCSI storage products.

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