Serial ATA and iSCSI
Storage networks fuel the distributed enterprise
THE MARRIAGE OF networking and storage technologies is not only simplifying the way storage is managed, it also promises to revolutionize the way enterprise storage is used, allowing corporate data to be pushed to the edge of the network to support Web services-based computing and pervasive access to information resources.
Two key ingredients in the mix are SATA (Serial ATA), a new disk storage interface that boosts the performance of low-cost NAS (network-attached storage) appliances, and iSCSI (Internet SCSI), a new protocol that will help companies build storage networks without the cost penalty of Fibre Channel.
For the past two decades, ATA (Advanced Technology Attachment) has provided reasonably priced and increasingly faster and larger disk drives. As ATA approached its technological limits, market leaders such as APT Technologies, Dell, IBM, Intel, Maxtor, and Seagate have joined forces to create SATA, a serial interface offering unprecedented performance for connecting to low-end storage devices, which will in time replace ATA .
Released in August 2001, SATA’s specifications include data transfer rates that start at 150MBps (increasing to 600MBps over time) and a combination of slim cables and compact connectors that gives PC and storage appliance manufacturers more flexibility when arranging storage components inside the box. In addition, SATA’s low-voltage signals facilitate the integration of embedded controllers into the motherboard.
Furthermore, each SATA device enjoys a dedicated connector to the host controller, which does away with the annoying necessity of sharing connections across master and slave drives, simplifying installation and eliminating the software overhead of managing multiple devices on the same cable.
Although SATA devices should maintain the affordable cost of ATA, its data transfer rates extend far beyond the range of 33MHz PCI; to take full advantage of SATA’s potential, companies will be forced to purchase more expensive machines with heftier I/O architecture, such as 66MHz PCI or PCI-X.
The iSCSI protocol should make SANs more affordable by using IP’s packet-based transport for storage instead of Fibre Channel. Although processing TCP/IP takes a significant toll on a server’s CPU, a new family of NICs (network interface cards) offers to offload that burden onto application-specific integrated circuits. Finally, with 10Gbps transfer rates on the horizon, iSCSI promises all the performance of Fibre Channel without the distance limitations or expensive conversions between protocols.
Although getting iSCSI started in your shop is likely to require the purchase of several new hardware devices such as GbE (Gigabit Ethernet) NICs and additional network switches, the overall implementation cost still has the potential to pay off over Fibre Channel. But here’s the catch: To prevent undesirable jams, storage traffic must flow on a dedicated network. So, unless you already have an exclusive path in place, implementing iSCSI will still require the expense of building one. Moreover, because of its vulnerability to magnetic and electrical interference, copper might prove to be an unreliable medium for storage networks.
These things considered, adopting iSCSI for your storage network will not guarantee huge savings over Fibre Channel. Nevertheless, iSCSI promises to be a worthy competitor to Fibre Channel, which is good for the storage market and good for storage customers.
