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Killer serial: is ATA ready for the enterprise?

IBM's Vojnovich says that most corporations start small. He expects first deployments to be in a specialty application or a remote office "to see if it has legs." This translates into lower-end departmental-level NAS or server platforms, he says. "This would be the guy with a fair amount of disk, but not data center amounts."

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A sampling of serial ATA products
Seagate: Barracuda 7200.7. Capacities: 160GB, 120GB, 80GB and 40GB; 7,200 rpm performance level, 8MB cache available on 160GB and 120GB - otherwise, 2MB cache.
Maxtor: Maxline II family of drives. Volume shipments with serial ATA are scheduled to begin in the Q103.
IBM: Deskstar family of drives has serial ATA in prototype drives.
Go Western Digital: Western Digital has nothing formally announced, although they plan to do something early next year.
Fujitsu: 2.5" serial ATA hard disk drives is currently available for samples for strategic partners.
LSI Logic: Family of high-performance Serial ATA MegaRAID adapters made up of MegaRAID Serial ATA 150-6 and the MegaRAID SATA 150-2. The products aren't shipping in volume yet.
Intel: Serial ATA Controller 31244, available 1Q 2003; Intel RAID Controller SRCS14L, available Q402.
3ware: Escalade 8500 family of serial ATA RAID controllers is currently shipping.
Adaptec: Serial ATA RAID controller begins shipping early 2003. First in family of serial ATA products, including external RAID subsystems for SANs, such as DuraStor Fibre Channel-to-serial ATA external RAID solution, which ships in the Q1 next year.
Promise Technology: SATA150 TX series of SATA controller cards shipped in December. Promise's FastTrak S150 family of ATA RAID controllers for serial ATA/150 drives will also ship in December.

Once serial ATA gains a toehold at the low end, the big question is whether its price/performance trade-offs will render it acceptable for high-end storage systems. "Arguments are intense as to how far up the storage food chain serial ATA will go," says Gartner's Monroe.

Most industry experts expect to see it first in low-end enterprise-class subsystems. For example, Zambeel Inc. will be rolling out a serial ATA version of its enterprise NAS system early next year, says Karl Schubert, the senior vice president of engineering at the Fremont, CA-based storage manufacturer. In fact, Schubert expects to see serial ATA in fairly high-level systems. "SCSI and Fibre Channel don't have to be the only solutions," he says. "If what you're doing requires a high OLTP rate, you'll use Fibre Channel. But the actual number of applications and quantity of disks for uses like that is relatively small, compared with the amount of data kept as file data and used for normal applications."

There, he says, serial ATA will do fine, particularly as the technology becomes seasoned. Schubert points out that similarly, parallel ATA was embraced by big companies such as Compaq and Dell as the technology became more reliable. "These guys went back to parallel ATA because of its price and value," he says.

SATA enables new applications
Serial ATA is a natural for disk-to-disk backup applications. Many experts expect to see serial ATA in what StorageTek calls the "mezzanine layer" of disk subsystems (i.e., above tape systems and below the very high-end storage systems).

Arun Taneja, a senior analyst at Enterprise Storage Group in Milford, MA, sees this storage niche booming in the near future. "We have a tsunami of new types of data that needs to be stored in different ways than transactional data," he says. New laws require Health Insurance Portability and Accountability Act of 1996 (HIPPA) and financial services data to be stored online, and recoverability needs to be in seconds, not days.

"A scenario like that begs for serial ATA," says Scott Robinson, the chief technology officer at Datalink, a storage outsourcer based in Minneapolis, MN. "Subsystem serial ATA for most applications will provide all the performance you need for less money. There's almost no reason to use a higher performance, higher priced subsystem if you have serial ATA," he says.

"We expect to have serial ATA at close to a penny a megabyte by middle of next year, says Robinson. Compare that with today's typical midrange RAID systems based on Fibre Channel. They're typically three to five cents per megabyte. If you back up terabytes of data, that price differential can be pretty dramatic," he says.

Robinson takes it one step further, saying that disk-to-disk serial ATA will soon be cheap enough to rival tape cartridges. "By 2005, he says, "the per-megabyte cost of ATA disks will be close to converging on the cost of tape cartridges."

Steve Luning, the director of storage architecture and technology at Dell's Enterprise Systems Group agrees, saying many vendors will start enhancing disk-to-disk backup features to be more competitive with today's disk-to-tape backup. "Clearly, putting tape in a box and putting it off-site isn't something you do with disk," he says. But if you want to replicate data for safety, it might make more sense to use a serial ATA farm of disks than a tape library. Of course, disks offer incremental backups and random access.

Luning pushes the possibilities of serial ATA even further, to what he calls disposable or self-healing storage. Says Luning: "Because serial ATA is so cheap, we can ship storage arrays with a few extra drives in them."

He envisions one scenario with a shelf of 15 drives. "You package 15, but only offer 13 for use. Any time a disk fails just switch over to one of the extras." This becomes feasible when technology is cheaper than service costs. Luning says that Dell is working on figuring out the price point at which this scenario will work.

Compatibility issues
Much has been made of the fact that serial ATA isn't backwards compatible with parallel ATA or SCSI. But is this really a big deal? Not for Datalink's Robinson: "It's not compatible from a hardware connectivity perspective, but it will be compatible for software drivers written for parallel if you get an adapter card, and those are coming out as we speak."

Serial's selling points
Serial ATA has several technical improvements over parallel ATA:
Serial instead of parallel bus. Serial has only four data lines compared with parallel ATA's 32, and data is put through in a serial fashion, enabling serial ATA to run at very high speeds: 150MB maximum transfer rate (300MB/600MB envisioned for the future).
Point-to-point connectivity. Serial ATA has a single cable between the controller and each drive, which means that each drive can talk to the controller without having to wait for other data traffic to clear first.
Simpler cabling. Instead of the dreaded flat ribbon cable with a 32-point connector, serial ATA will have a six-pin connector and a small round cable, making it much more manageable inside a server, as well as improving performance and scalability.
Hot-pluggability. You can swap out a drive on a server without having to power down the entire machine, which saves significant maintenance time.

"With an adapter in front of those drives, I don't see a lot of difference," says Zambeel's Schubert. "The attractiveness of serial ATA is still greater than the pain of incompatibility, he says, adding that the cost/benefit ratio is clearly in the right direction."

Others, however, point out some possible complications. Gartner's Monroe, for one, is skeptical that the resolution of the software issue is as simple as an adapter card, particularly on direct-attached storage (DAS). He says that the drive manufacturers all maintain thousands of lines of propriety microcode for each family of drives. "For one family of SCSI drives, Seagate may maintain 20 different versions of microcode to satisfy the various requirements of OEMs," he says. DAS systems are more likely than fabric-attached storage (FAS) to use this microcode to fine tune the drive characteristics with the peculiarities of the system. "It's going to be very hard to plug-and-play replacements in that kind of environment," Monroe says. "On the other hand, if you're connecting to FAS, it's going to be pretty easy to use serial ATA instead of SCSI internally on the other side of the subsystem."

Vojnovich raises another issue when he suggests that migrating data from SCSI to serial ATA drives could also present problems. When you migrate data from legacy systems, the issue becomes the intelligence that's managing the disk, he says.

"As far as old files on parallel ATA, there are tools to help move them over: mirroring, backing up to tape and restoring it to a new unit." The two technologies' similarities make migration a relatively simple matter. "But if somebody wanted to take data on SCSI and read all the blocks onto serial ATA, that would be somewhat of a challenge," he says. "The formats and protocols would be difficult to reconcile."

Whatever the difficulties, it's clear serial ATA drives will have a significant presence in the storage markets in the near future. Monroe predicts the technology will hold 30% of the enterprise market by 2005.

"As we come out of this bad economy, there will be a lot of pent-up demand, but not much budget," says Monroe. Storage budgets will be scrutinized far more closely. "Instead of one level of sign off, you might have five and if you're not proposing the least expensive option that will solve the problem, you'll have to prove why," he says.

This was first published in January 2003

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