Tape market embraces RAID
By Heidi Biggar
One by one, tape drive manufacturers and library vendors are stepping up to the plate with tape RAID offerings. Though still in its infancy, tape RAID is expected to become increasingly popular over the next couple of years.
But for now, says Bob Abraham, vice president of Freeman Associates, an industry research firm in Santa Barbara, CA, you should expect "only a small up-tick in the popularity of these systems for the sheer purpose of increasing transfer rates."
Tape RAID is still a niche product, primarily targeting high-end applications. Nonetheless, for users requiring high data availability, high performance, or fault tolerance, it is an exciting option.
As a concept, tape RAID is not new. It has been around for many years in, for example, supercomputer environments. "The companies that used it first were looking for very high transfer rates," says Abraham, "so they would take 19mm or 3480/3490 tape drives and put them together and basically multiply the transfer rate. They didn`t really care about capacity."
Today, the same concept applies, though in a scaled-down fashion. Vendors such as ADIC, Compaq, Overland Data, and Procom are taking lower-cost, higher-performance drives such as DLT and AIT and putting them together in parallel to increase data rates and capacities.
For example, Procom last month began shipping a five-drive tape array that can be configured with either AIT or DLT7000 drives or AIT autoloaders. The Tape Array 100, says Mike Khoyilar, tape product manager at Procom, "addresses high capacity, data availability, and throughput." Similarly, ADIC combines five DLT4000 or 7000 drives into a 19-inch-rack in its Tape Array 5.
Though some manufacturers are marketing these tape arrays as RAID-like products, they lack true RAID functionality. Steve Scully, business line manager for performance libraries at Exabyte, says that "a number of companies just produce tape arrays, which in a lot of cases are just four, five or seven drives in a single box, but they are controlled independently. The packaging is just a convenience, and there really is no increased functionality."
Tape arrays that provide RAID functionality--albeit at a much more immature level than disk RAID--are often referred to as true RAIT (redundant array of independent tape drives). These types of systems are just starting to emerge.
At Comdex in November, several manufacturers displayed RAIT systems. Sony, for example, showed an array of full-height 5.25-inch AIT autoloaders packaged in JMR enclosures and connected to an Ultera (Laguna Hills, CA) Striper RAID controller. Exabyte exhibited a small, two-drive mirroring RAIT configuration with a RAID controller. Exabyte also offers an integrated solution with two Mammoth drives, and is working on an autoloader array.
"It`s the second Comdex we`ve brought a tape RAID box to," says Exabyte`s Scully. "We`re still trying to see if there`s really a solid market to go after." Scully reports no marked increase in customer interest. "There is some interest in the performance characteristics of tape RAID, but the limiting factor is still software support from a media management point of view," he says.
This opinion is echoed at other vendors. For example, Dave Glatfelter, product marketing manager of library software at StorageTek, thinks there is still a lot of software that`s needed to manage both the library and media aspects of tape RAID products. "Traditional backup software is supposed to handle that, but it doesn`t," he contends. Nonetheless, StorageTek has joined the tape RAID bandwagon and is pursuing both hardware and software RAIL (redundant array of independent libraries) solutions.
RAIL heats up
RAIL is expected to be the next phase of tape RAID, with interest greatest among those looking to improve system redundancy. However, the concept is also appealing to users demanding very high performance (e.g., space telemetry and government/military applications).
One of the first RAIL systems was demonstrated by StorageTek last spring. The system included three libraries and CA`s ARCserve software. Later this year, STK is expected to unveil a low-end offering--centered around its Timberwolf family--for NT and small Unix environments. On the high end, STK is working on a fault-tolerant system based on 9840 and larger libraries.
Elsewhere in the industry, Exabyte shipped a 6-drive, 90-slot Arrowhead library with RAID functionality last September; a 10-drive, 200-cartridge Mammoth-based version is expected in March.
Hardware or software?
Tape RAID functionality is available in both hardware and software implementations. On the hardware front, ATL recently announced a Fibre Channel card (based on an off-the-shelf host adapter from QLogic) that works in tandem with a proprietary tape RAID controller. The board will be integrated into ATL P1000 libraries.
"Data comes in through the Fibre Channel adapter and onto a standard PCI bus," explains Frank Berry, director of business development at ATL. "It then goes onto the library RAID controller, which bridges Fibre Channel to SCSI and handles functions like mirroring, striping, etc."
The controller can support two Fibre Channel connections, and a 160MBps bandwidth. For now RAID controller will only support RAID1 (mirroring), but users will be able to upgrade to RAID3 by year-end. The controller is priced at $10,000.
Also on the hardware front, Ultera Systems will release Ultra2/LVD Striper and Reflection (mirroring) controllers in March, and Fibre Channel versions late this summer. Ultra2/LVD will boost bandwidth from 40MBps to 80MBps; with Fibre Channel, bandwidth will jump to 160MBps (Striper series only).
Not surprisingly, at $6,000 (Striper) and $4,000 (Reflection), the cost of these products is significantly higher than software alternatives like Seagate`s RAIDirector or Computer Associates` ARCserve.
Says Mo Nour, president of Ultera: "Hardware approaches can`t match the low cost of software, but software approaches can`t match the performance and functionality of hardware implementations." Software solutions require separate host adapters for each drive connection. At $500 or $600 per adapter, the overall cost of software solutions rises significantly. Drives can be daisy chained to one host adapter; however, doing so defeats the purpose of implementing a RAIT solution since drives then have to be accessed one at a time.
Platform support is a key distinguishing feature between hardware and software implementations. Unlike software packages like RAIDirector and ARCserve, which only work in NT environments, hardware solutions are platform independent.
For Vance Buffalo, systems administrator at Ameren Corp., an electric utility company in the Midwest, this was the determining factor in his decision to install a hardware tape RAID solution: "There were no software options available. Most of the tape backup companies we talked to could do cloning for open systems (Unix, NT, and Novell), but they did not offer mirroring." Ameren uses a mirroring configuration with an Ultera Reflection controller to make two copies of its mission-critical data.
Despite this limitation, Seagate has reportedly seen ramping sales of its RAIDirector product, which began shipping last September. Much of the excitement, according to company officials, has been from tape array manufacturers. Though Seagate is currently focusing on the NT arena, the company is working on achieving similar functionality on other platforms such as Unix and NetWare.
Whether RAIT or RAIL, software or hardware, the management issues of tape RAID are anything but simple. Vendors such as Microsoft and Legato are working on library management software applications to ease some of these pains, but a solution is reportedly at least a year away.