SATA drives product roundup

SATA drives work the same way as Fibre Channel (FC) or SCSI drives, except that SATA uses a less expensive protocol and is less expensive to implement. The low price of SATA is its allure, and its popularity in the IT industry is growing quickly. The downside? SATA is slow and is not a good fit for primary storage. Instead, its sweet spot is secondary storage, because of its massive capacity compared to FC and SCSI.

This product roundup discusses how SATA drives are evolving, how they are used and who is using them.

Definition
SATA is a standard for connecting hard drives into computer systems. As its name implies, SATA is based on serial signaling technology, unlike current IDE (Integrated Drive Electronics) hard drives that use parallel signaling.

SATA has several advantages over the parallel signaling (also called Parallel ATA or PATA) that has been used in hard drives since the 1980s. SATA cables are more flexible and thinner than the massive ribbon cables required for PATA hard drives. SATA cables are also much longer than PATA ribbon cables, allowing the designer more leeway in the physical layout of a system.

What SATA drives do best is provide a middle ground between FC or SCSI disk, which is lightning fast but expensive, and tape, which has high capacity at a low price, but slow retrieval. "SATA drives have definitely made disk more affordable," said Arun Taneja, consulting analyst and founder of the Taneja Group. "It is mostly used for secondary storage, where data is kept for a week or so for short-term recovery."

Taneja added that SATA may not be as cheap as tape, but the price has dipped enough that the TCO is on par with or even lower than tape, which can bog down users with media errors and management.

Key vendors and products
The big SATA vendors are Maxtor Corp., Seagate Technology LLP, Western Digital Corp. and Hitachi Data Systems Corp. Drives are often marketed directly to users, usually for adding capacity to individual systems. On a larger scale, storage vendors buy SATA drives and put them into their own systems.

SATA is used extensively in desktop and laptops, servers and disk subsystems. Because SATA was designed for capacity, it does not have fast rotational speed, spinning at roughly half the speed of FC and SCSI drives. "SATA is made with cheaper parts and components, so it can't match the speed, reliability and endurance of FC or SCSI," Taneja said. But with the amount of data constantly growing, "no one can afford to put it all on high-end disk. So now you see everyone from midsized companies to large enterprises using SATA to store data that is not mission-critical," Taneja said.

Innovations and trends
With over three times the capacity per drive as FC drives, at one quarter the price, it's easy to understand the appeal of SATA.

Randy Kerns, senior partner at the Evaluator Group, concurred that SATA drives are common for storage that does not demand high performance, but he added that SATA doesn't necessarily save companies money just because the drives are cheaper than FC or SCSI. The bigger issue is controlling data placement.

"If a company has only SATA drives, then data placement is not a problem, and the company saves money," Kerns said. "But if they mix high-performance and low-performance drives, then they have to control data placement. Unless they have some automation capability to handle the placement, then it must be done manually. This creates an administrative cost that's probably more than the company saved by buying SATA."

Probably the most recent development in SATA, according to Kerns, is native command queuing (NCQ), a command protocol for SATA that makes it possible to have several outstanding commands within a drive at the same time.

A SATA drive that supports NCQ has an internal queue in which commands can be rescheduled and reordered. NCQ includes a tracking mechanism for both pending and completed portions of the drive workload and can let the host issue more commands to the drive while the drive looks for another command.

Another possible trend, according to Taneja: SATA will be challenging the speed and reliability of FC and SCSI drives in the near future because of a chip technology being developed by companies such as Sierra Logic Inc. and Ario Data Networks. Sierra Logic calls its product Silicon Storage Router. The router is actually a chip that sits between SATA drives and a RAID controller and provides FC features such as scalable routing and full-path redundancy. It's designed to make SATA drives reliable enough to be used for primary storage.

Other vendors with similar chip-based products are Marvell Technology Group Ltd., Broadcom Corp. and PMC-Sierra Inc.

Taneja predicts that this technology is the beginning of SATA's entrance into the enterprise. "These inexpensive chips sitting inside SATA drives will narrow the gap between SATA and FC and SCSI in the next two years," he said.

More information on SATA Drives:
How to get SCSI reliability on a SATA budget
Plan before you implement SATA
Top 10 low-cost storage alerts of 2004
Should you choose a SATA-based array?
How to prevent common problems in SATA drives
The advantages of SATA II over SATA I
Learning Guide: Low-cost storage