A standard protocol for decades, SCSI (Small Computer Systems Interface), enables computers to communicate with storage devices. As system interconnects move from the classic bus structure to a network structure, SCSI commands must be mapped to network transport protocols. Today’s IP Gigabit networks meet the performance requirements to seamlessly transport SCSI commands between application servers to centralized storage.
The iSCSI protocol enables the transfer of SCSI packets over a TCP/IP (Ethernet) network. iSCSI is an interoperable solution which enables the use of existing TCP/IP infrastructure and addresses distance limitations; iSCSI can also be used over the Internet. This means the disk drives in your SAN are presented over your existing Ethernet network to server applications as though the disks are local to your physical server hardware.
Don’t confuse this with traditional SCSI disks; in fact, iSCSI storage is typically implemented with affordable SATA or SAS disks. iSCSI presents block-based storage resembling your internal disk drives, whereas a NAS is nothing more than a plain file server that presents storage as file shares. A common scenario is to use a portion of your iSCSI SAN storage as back-end disks for file servers (NAS), consolidating both application data and file shares into one appliance.
With iSCSI storage you can use any IP switches and routers, and the client machines (your servers) can use a software driver called an “initiator” instead of the more costly FC HBAs (Host Based Adapters). For older servers with lower-powered CPUs you can use an iSCSI HBA, which is still lower cost than a FC HBA. Microsoft provides freely downloadable software iSCSI Initiators and endorses iSCSI technology for Windows, helping to promote iSCSI awareness. The concept of using an IP network for block-based storage causes many people to incorrectly assume storage traffic will clutter their LAN, or that IP networking may not provide the necessary performance your applications require. While it is true that many early iSCSI vendors were shipping products that were not up to the job of enterprise class applications such as Microsoft Exchange, VMware and SQL Server, there is also a well-established base of vendors that are shipping iSCSI storage into SMBs and enterprise customers.
The iSCSI protocol provides numerous benefits for SANs vs Fiber Channel, a few key points are summarized below:
- iSCSI uses familiar networking standards (Ethernet and TCP/IP): Most IT administrators are already familiar with TCP/IP, unlike the more complex skills required for FC storage.
- Total storage costs are reduced: iSCSI SANs are easier to install and maintain than FC, lowering installation and maintenance expenses. iSCSI reduces the necessity of hiring or outsourcing
- Replication works over a standard IP network: iSCSI replication eliminates distance limitations and costs associated with FC routers.
- Reduces complexity by eliminating FC switches and cabling: Using standard Ethernet switches simplifies everything as most organizations already have in-house IP networking skills.
- iSCSI scales to 10 Gigabit: For enterprise applications that require high transactional performance 10GigE is available, thus expanding iSCSI Storage Networks’ performance to equal the performance of Metro and Wide Area Networks.
iSCSI’s use of IP Networking means long distance is no longer an issue for backing up remote sites or performing disaster recovery. With the use of Secure Internet Protocol (IPSec) and Secure Sockets Layer (SSL) to provide authentication and privacy, iSCSI over a public network is a viable method to extend the corporate network without incurring high costs.10 Gigabit Ethernet provides enough bandwidth and iSCSI allows any IT administrator to easily deploy a true SAN over an IP network.