Network-Attached Storage (NAS)
NAS devices share their storage resources with other clients on the network, in the form of file “shares.” The clients read and write files on the NAS server using either SMB/CIFS or NFS file protocols. The NAS device has its own storage and internally uses block I/O to store the data in its own internal format. NAS devices typically can have many file “shares” and can potentially be a great physical distance from the network clients.
Storage Area Network (SAN)
SAN architecture, using “block” I/O, can be implemented over an Ethernet network or a Fibre Channel (FC) network, each having its own strengths and weaknesses.
Ethernet networks are ubiquitous, relatively inexpensive, and they offer a wide variety of choices of built-in, as well as peripheral network hardware solutions. The least expensive solutions use copper cabling and connections. Ethernet networks using TCP/IP protocol typically manage network traffic with software and frequent interrupts to the host computer.
By comparison, Fibre Channel networks tend to be more expensive, because they use dedicated fiber-optic technology, they are physically separate from the local Ethernet network, and they require specialized expertise. FC host bus adapters (HBAs), managed switches, and optical networks are dedicated to block level storage I/O. FC networks manage traffic using highly efficient hardware processing that offloads functionality from the host CPU.
SAN architectures use block SCSI protocol for sending and receiving storage data over their respective networks. Fibre Channel (FC) SANs implement the SCSI protocol within the FC frames. Internet SCSI (iSCSI) SANs implement the same SCSI protocol within TCP/IP packets. Because both technologies allow applications to access storage using the same SCSI command protocol, it is possible to use both technologies in the same enterprise, or move from one to the other.
For the larger enterprises that have implemented SAN technology, most have implemented Fibre Channel technology. These enterprises typically demand proven technology, have the need for high bandwidth storage solutions, have the budgets to pay for more expensive hardware to meet their performance and reliability needs, and typically have full-time staff dedicated to storage management.
Some organizations have implemented only Fibre Channel SANs into production use. Some organizations have implemented only iSCSI SANs into production use. Some organizations have chosen to implement Fibre Channel SANs and iSCSI SANs. An iSCSI connection can be used to bridge a server into a Fibre Channel SAN. In many cases, iSCSI SANs can be deployed more quickly than Fibre Channel SANs.
Many disk storage solutions available today offer both Fiber Channel and iSCSI interfaces into the same disk subsystem. Many iSCSI-only solutions use the same high-end components in the disk subsystem as the Fibre Channel-only solutions. These design and implementation factors reduce or eliminate concerns about performance and reliability of iSCSI storage solutions.
IP-based SAN technology such as iSCSI has not yet been deployed as widely as Fibre Channel SAN technology, in part, because it is a newer technology. But iSCSI SAN technology has been proven to work reliably, provide excellent performance, and is a cost-effective choice for many storage environments.
A typical SAN environment consists of one or more application servers, one or more storage devices, a switch between the servers and the storage, the appropriate external hardware interface in the application server, and appropriate cabling.
The components of an iSCSI SAN are equivalent in concept to those found in a Fibre Channel SAN, but typically are less expensive. However, there is a reason for the difference in price of the hardware components. Fibre Channel switches and host bus adapters almost always use managed switches and fiber optic technology including cables, connectors, transceivers, etc., which are more expensive than the typical copper-based technology found in Category 5, 5e, or 6 Ethernet cables, standard NIC cards and unmanaged Ethernet switches. The price differences begin to diminish when comparing fully managed fiber-optic Ethernet and Fibre Channel environments. The line rates found in the Fibre Channel environments are 1, 2, and 4 Gbps. The line rates found in typical Ethernet environments are 1 Gbps or less.
When comparing costs of Fibre Channel and iSCSI storage solutions, it is important to include advanced storage and management functions in the calculations. Many of the iSCSI solutions have done a good job of simplifying common functions such as LUN provisioning and provide advanced storage and management functions in the solution for less cost than other types of solutions.
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