Mastering a moving market

The standards situation in the technology industry is generally so loose that it long ago became the target of jokes. For example, one goes, "What's the nice thing about standards? There are so many to choose from." The storage market is no exception.

There are three main standards for enterprise-class disk drives, not to mention the earlier iterations that can be found in the designs of countless new products still being sold. But this diversity wasn't always the case.

Not long ago, when storage was still a back-burner issue for most information technology managers, options were scarce for standards-based storage gear. You had the prevailing product type from vendor A, or the same prevailing product type from vendor B or C. But you didn't expect the two products to work together.

Storage standards recently have become more plentiful and meaningful — not only in terms of actually making vendors' products more compatible, but also in the way they drive different approaches to solving common data storage and management problems.

Federal Computer Week asked leading storage industry analysts about some of the storage standards that will be most important as the industry moves ahead.

Serial Attached SCSI

With the first products hitting the market at the end of June, Serial Attached SCSI (SAS) is the newest kid on the storage block. SCSI itself, however, is hardly new. It has been the industry's dominant interface for production-class disk drives for more than a decade.

SCSI, properly called parallel SCSI, uses shared bus architecture. In its current top version, Ultra320, the parallel SCSI family has hit its performance wall at 320M throughput.

In addition, its data transfer bus supports connections for only 15 devices, although in practical terms the limit is far less, because the bus would be overwhelmed if that many devices were trying to push data through simultaneously.

"Parallel SCSI is simply maxed out," said Mike Karp, senior analyst at Enterprise Management Associates.

When vendors anticipated the problem four years ago, they began work on the next-generation SCSI. The result is SAS, a serial technology that debuts at 3 gigabits/sec. When factoring in the practical differences between parallel and serial interfaces, SAS roughly picks up where parallel SCSI ends.

However, SAS will shoot up to 6 gigabits/sec by 2007 and then 12 gigabits/sec a few years later.

Vendors also will offer SAS drives in fast 10,000 and 15,000 rpm models, which will be suitable for applications that must move a lot of data. The first SAS drives will be offered in 36G and 73G capacities.

SAS comes in two sizes, the standard 3.5-inch and a new 2.5-inch version. Vendors will use the 2.5-inch drives to pack more storage and performance (more spindles and armatures) into a single storage system cabinet, which means you use less data center floor space for the same amount of storage. The 3.5-inch drives will serve as replacements for equipment designed with parallel SCSI disks in mind.

SAS provides other goodies. Because it is a serial technology, each device offers the benefit of the full bandwidth in a point-to-point topology, without the device contention problems of the older parallel SCSI. Through the use of extenders, which are mini-switches, thousands of SAS drives can be linked.

SAS also operates in duplex mode, which allows the drive to handle inbound and outbound streams simultaneously at full bandwidth. Lastly, drives can be dual ported, and the redundant connection is a key requirement for high availability.

Data center managers should have few objections to SAS. "One nice thing about SAS is that it is compatible with what you already have," said Greg Schulz, senior analyst at the Evaluator Group.

SAS uses the same command set as the parallel SCSI devices, so managers do not have to modify their current storage infrastructures when introducing SAS. Even the pricing of SAS will be comparable to SCSI.

Looking ahead, SAS is compatible with lesser-performing but less expensive Serial Advanced Technology Attachment (ATA) drives, which have been taking the enterprise storage market by storm. Expect to see manufacturers creating arrays containing both SAS and Serial ATA drives. This would allow an organization to do tiered storage within a single storage box by directing data requiring high performance to the SAS drives and keeping data with less demanding requirements on the low-cost Serial ATA drives.

However, the real goal for SAS is to rival Fibre Channel disks at the enterprise level. "SAS will give you a lot of enterprise capabilities, but it will be less costly than Fibre Channel," said Scott Robinson, chief technology officer at DataLink, a storage systems integrator.

Serial ATA

About a year ago, Serial ATA was the first drive to popularize the serial storage interface. ATA, also known as IDE, was the PC disk drive standard for years. At 7,200 rpm, the drives are slow and not intended for heavy-duty cycles, but they cost much less than SCSI or Fibre Channel drives.

As Serial ATA began flooding into the market, storage vendors quickly began assembling large numbers of high-capacity Serial ATA drives into Redundant Array of Independent Disks (RAID) configurations to deliver large amounts of low-cost disk capacity.

Those arrays have become popular with network-attached storage systems, archiving and content-serving applications.

Serial ATA "is cheap and good enough," Schulz said.

Such drives tend to be less reliable than their more costly rivals, but for many situations it may not matter. And when it does matter, an organization could opt to throw large quantities of Serial ATA drives at a problem.

Some of the newest disk array products are using the very reliable RAID 6 for this purpose, because arrays configured this way can recover without interruption even if a couple of drives fail simultaneously.

"With [Serial ATA], we can get eight times more capacity for less money," said Ralph Miles, network administrator at the Air Force Center for Environmental Excellence. "Users don't notice the slower speed, and with RAID, I'm still protected in case of a failure."

Fibre Channel

Fibre Channel is clearly under attack. It is well-established as the choice for high performance and production-class enterprise storage, but Fibre Channel disk drives now face serious competition from SAS.

Besides its service as a disk interface, Fibre Channel also plays a critical role as the networking technology in the storage-area networks (SANs) that have become fixtures in most large government data centers.

On this front, Fibre Channel is being threatened by the rise of Internet SCSI (iSCSI), an alternative method for building SANs that uses general-purpose, standard IP-based Ethernet gear instead of the more costly Fibre Channel equipment.

But for now Fibre Channel still holds the performance advantage, strengthened by the recent introduction of a 4 gigabits/ sec version. Fibre Channel's performance edge will take a hit when 10 gigabits/sec Ethernet takes off, though even faster Fibre Channel specs are on the development road map.

"I don't see Fibre Channel networking going away very soon," Robinson said. The technology is already well entrenched in large enterprises, which will be reluctant to rip it out without a good reason, he said.

Fibre Channel may be costly and complicated to deploy, but once it is working right, it provides significant benefits. In addition to speed, "it is very reliable and provides predictable performance," said Dianne McAdam, senior analyst and partner at the Data Mobility Group.

Despite its ubiquity in the enterprise data center, any thoughts of pushing Fibre Channel down to the midlevel market have probably been dashed by the rise of iSCSI and SAS, analysts say.

Radding is a freelance journalist based in Newton, Mass. He can be reached at alan@radding.net.