What Internet Scsi (Iscsi) Is; Iscsi Components - IBM TotalStorage DS300 Best Practices Manual

2.1 What Internet SCSI (iSCSI) is

Internet SCSI (iSCSI) is a transport protocol that carries SCSI commands from
an initiator to a target. It is a data storage networking protocol that transports
standard Small Computer System Interface (SCSI) block I/O protocol requests
(commands, sequences and attributes) over the standard Transmission Control
Protocol/Internet Protocol (TCP/IP) networking technology. SCSI data and
commands are encapsulated in TCP/IP packets. iSCSI enables the
implementation of IP-based Storage Area Networks (SANs), enabling customers
to use the same networking technologies—from the box level to the Internet—for
both storage and data networks. Taking this approach enables users to get full
access to IP management and routing, and, as it uses TCP/IP, iSCSI is also well
suited to run over almost any physical network. By eliminating the need for a
second network technology just for storage, iSCSI can lower the costs of
deploying networked storage and increase its potential market. ISCSI is a native
IP interconnect that wraps SCSI data and commands in TCP/IP packets. The
receiving device takes the command out of the IP packet and passes it to the
SCSI controller, which forwards the request to the storage device. Once the data
is retrieved, they are again wrapped in an IP packet and returned to the
requesting device.
The main advantages of iSCSI are, when compared to a Fibre Channel
installation, it is a low cost implementation, and there are no distance limitations.
There are some drawbacks to iSCSI. An IP network is based on design
considerations different from those of storage concepts. The TCP/IP protocol is
software-based and geared towards unsolicited packets, whereas storage
protocols are hardware based and use solicited packets. Latency, introduced
when putting storage on the same route as other network traffic, and security
have been concerns for iSCSI. Additional latency is introduced because of the
greater amount of processing to be done within the iSCSI chip to support TCP.

2.2 iSCSI components

iSCSI consists of several parts to provide a total solution. Figure 2-1 on page 13
shows the different pieces that may appear in an iSCSI environment.
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IBM TotalStorage DS300 and DS400 Best Practices Guide