Saturday, January 12, 2008

Concept :: All about iSCSI !

I am compiling a list of common FAQ's to understand iSCSI better .

1 . What is iSCSI?
iSCSI is based upon existing industry standards, practises and applications that are known and understood by end users.
iSCSI is a network storage protocol that encompasses block level SCSI data in a TCP/IP frame, thus allowing servers to access storage resources over an existing IP infrastructure.
iSCSI is a combination of SCSI and Ethernet technologies that have been around for more than 20 years and are fully tried and tested.
iSCSI is a cost effective way to build SAN’s at much lower cost point, giving users greater consolidation in their environment.

2 . What is an iSCSI Appliance?
Our iSCSI Appliance has lots of disk storage attached. This disk can be SATA, FC or SCSI based. The iSCSI Appliance also has multiple Gigabit cards for sustaining the transfer rates that are required by the servers on the network. The Appliance also offers a high degree of redundancy against component failure and typically two or more processors.
In addition to this Snapshots can be taken for the disk being offered up along with mirroring and high availability.

3 . What are the drawbacks of Fibre Channel compared to iSCSI?
Fibre Channel is still viewed as an alien architecture. It requires special training and high-priced expertise to keep a Fibre Channel fabric operational. Fibre Channel also requires its own management software, which is not fully integrated with mainstream IP network management. So, although Fibre Channel fabrics have many technical strengths, overall they require additional skill sets and tools.

4 . Do you think packet loss will be an issue in IP storage protocols?
Packet or frame loss also can occur in Fibre Channel fabrics if links are over-subscribed or poorly implemented. For IP storage, the TCP session control will insure that there is recovery from packet loss, should it occur. However, if the network is properly designed, this recovery mechanism won't be invoked frequently. I doubt that many users will start putting mission-critical IP storage data over congested or lossy network links.

5 . Which in your view will succeed, in order over time, between FCIP, iFCP and iSCSI and why?
Good question. We will see all three protocols used initially, but I think that over time you will see FCIP fall out of favor. FCIP is just FC tunneling and it perpetuates a lot of the problems associated with large or extended Fibre Channel fabrics. The more FCIP products deployed, the more these issues will surface and customers will look at alternatives.
iSCSI may gradually displace Fibre Channel, both as a transport protocol and as an interface for storage devices.

6 . Is there a difference between an iSCSI HBA and an iSCSI NIC?
The iSCSI adapter vendors are all in a toot about what to call these things. Companies from the IP space like Alacritech or Intel are content to call them iSCSI NICs. Companies from the Fibre Channel space like QLogic want to call them iSCSI HBAs. The acronym "NIC" seems to have a commodity connotation, whereas "HBA" implies some additional value.

7 . How would you define how iSCSI works in layman's terms?
Information that is key to modern business is ultimately stored on disk in the form of blocks of data. That block data is written to and read from disk using the SCSI protocol, which is optimized for low-overhead movement of data from disks to file servers, application servers or workstations. The iSCSI protocol carries those SCSI commands for reads and writes of data to disk using TCP/IP.
In short, for the layman, iSCSI simplifies storing or retrieving of blocks of data by using familiar, well-understood IP networking protocols and infrastructure and traditional SCSI commands.