A new technology that has been making some headlines is iSCSI. It is an alternative to FiberChannel for building SANs. The primary advantage is everything is IP which most sysadmins already know and love. Expensive FiberChannel HBAs and switches are not required and iSCSI SANs can be built by the home entheusiast reasonably easily.

In an ideal SAN environment which could have a mix of Linux/NetWare/Windows/AIX/Solaris environment, what is required is a solution that would work with everything. iSCSI supports all of these operating systems.

Today, iSCISI storage product development is taking two different paths in our industry.

One approach is based on developing an ISCSI-based storage “appliance.” These devices attach directly to the LAN, use ISCSI technology, and have imbedded storage in the device.

The second approach utilizes a gateway that provides the ISCSI technology and then front ends storage devices directly or in some cases, will “bridge” to Fibre Channel SANs, thus providing linkage from the Fibre Channel SAN environment to the IP LAN environment. Each of these approaches requires three separate components:

Initiators

These are the device drivers residing on the client, which route the SCSI commands over the IP network and provides access to the target device. These initiators drive the initiation of the SCSI request over TCP/IP.

Target Software

This receives SCSI commands from the IP network, and can also provide configuration support, storage management support, and so on. This is microcode that provides support for configuration, SCSI request handling, storage management, and so on. This microcode is built on a Linux 2.4-base kernel and is bundled with the storage appliance hardware.

Target Hardware

This can be a storage appliance that has imbedded storage in it. This can also be a gateway or bridge product, which has no internal storage of its own.