|
|
|
|
|
|
|
| Tape Market Embraces RAID |
|
| By Heidi Biggar - InfoStor, (for original article,
click here) |
|
| 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. |
|
| Article
Date: |
InfoStor
- January, 1999 |
| Magazine
Volume: |
3 |
| Issue: |
1 |
|
|
|
Back to
Articles of Interest |
|
