Trumping tape

In the ongoing struggle to automate and speed data backups and restores, storage administrators are increasingly turning to Advanced Technology Attachment disk subsystems. Now two vendors are pitching the idea of using specialized ATA disk backup appliances as an alternative to robotic tape autoloaders for handling large volumes of archival storage. Both are using specialized ATA disk array technology to lower the cost per gigabyte of disk-based storage and extend the life of backup disk drives, making them more attractive for archival and near-line storage.

The vendors, start-up Copan Systems and California-based Exavio, claim that this new technology, dubbed MAID, for massive arrays of idle disks, is competitive with tape and offers faster and more reliable access to data. MAID systems use arrays of ATA disk drives that power down when idle in an effort to extend media life. By spinning up only when they write or read data, the arrays use less power, mitigating heat issues and allowing drives to be packed more densely into the system. Idle disk drives require about 10 seconds to spin up, but once online, they provide faster access to archived data than tape does.

Although powering up disks as needed can extend useful life, disks that remain inactive for long periods tend to develop problems spinning up. To avoid this, MAID arrays can periodically power up all drives to relubricate the mechanics, Copan says. Drives are hot-swappable, and the systems support RAID for fault tolerance. Prices range from US$3 to $5 per gigabyte, depending on the configuration, the amount of redundancy and total capacity.

Steve Curry, architect for storage operations at Yahoo US, is considering buying Copan's Revolution 200T MAID array to cut the use of some 350 tape drives by half. By doing so, he hopes to improve reliability. "We see (one or two tape drive) failures every day. To us, it's not superunreliable, but it still has mechanical properties and does break down, which requires manual intervention," Curry says.

Archiving to MAID

Today Yahoo ships archival tapes to an underground storage facility run by Boston-based Iron Mountain. Curry wants to locate a MAID array at the backup facility and archive to it directly using a Fibre Channel or Fibre Channel-over-IP link. "From our calculations, it's looking like it's doable. We are just waiting for someone to build a product that works as advertised," he says.

Copan's 200T, announced in April, emulates a virtual tape library. It will scale to 224TB and restore 2.4TB of data per hour -- about five times faster than tape access speeds -- while keeping only one in every four drives powered up and online at any one time. The basic 56TB configuration, which includes 224 7,200 rpm, 250GB Serial ATA disk drives mounted in a single rack, will ship in the third quarter and sell for $196,000, or about $3.50 per gigabyte, according to Aloke Guha, Copan's chief technology officer.

Exavio's ExaVault array is primarily marketed as a device for near-line storage and streaming of multimedia content, although the company claims that the array can also emulate a tape backup system. ExaVault, available now, uses 300GB, 5,400 rpm and parallel ATA disk drives arranged in a single rack with one controller and a Fibre Channel or Gigabit Ethernet interface. Configurations range from 3TB to 120TB. A basic unit including a controller and 3.6TB of storage is $27,700; additional modules are $6,600 per terabyte, says Kevin Hsu, Exavio's director of marketing and product management.

Despite MAID's advantages, digital tape libraries remain the cheaper form of storage, at about $1.25 to $4.50 per gigabyte, according to Fred Moore, president of Horison Information Strategies. The low cost of tape and the fact that tape cartridges can be easily removed and stored off-site are the medium's most attractive features. In contrast, the individual disk drives that make up MAID appliances are bulkier and more fragile.

Hsu acknowledges that MAID systems cost more per gigabyte than tape libraries but argues that they are less expensive to run overall. "Terabyte for terabyte, tape is cheaper than MAID. If you look at total cost of ownership . . . you have to look at robotics, manpower, replacing the tape heads, maintenance costs. MAID is cheaper," he says.

Robert Amatruda, an analyst at IDC, disagrees, saying that tape still provides a lower total cost of ownership overall. "You're looking at a lot less money. It's still a compelling solution," he says.

Both Exavio and Copan are developing portable versions of their systems. Copan, for example, is working on special shock-proof disk enclosures that could be transported off-site. Drives would be stored remotely in a Revolution 200T shell chassis that would spin up the drives periodically to keep them conditioned for use.

But Amatruda eyes such portability designs with skepticism. "You drop some of that stuff and there could be data integrity issues," he says. "At the end of the day, disk and tape will play a complementary role."

At a glance: Massive Arrays ofIdle Disks (MAID)

  • What it is: Low-cost disk-based backup and archiving appliances that power down idle disks to extend media life. Lower power requirements and less heat allow for more compact, lower-cost designs.
  • Pros: Faster and more reliable than tape libraries.
  • Cons: Cost and portability. At US$3 to $5 per gigabyte, MAID still costs more than tape libraries. Disk media aren't well suited for off-site storage.

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