September 1998
Performance Breakthroughs Bring Excitement to Tape
Expanding storage creates problems for managers who must back up the systems under their care. Tape drive manufacturers are responding with new standards and enhancements like Super DLT and memory in cartridge.
IBM, HP and Seagate are working on a new tape standard called Linear
Tape Open (LTO). Quantum is working on their next-generation technology,
SuperDLT. Quarter-inch-tape makers like Imation and Tandberg are staying
ahead of Moore's Law by doubling tape storage capacity every year. Sony's
AIT format, with its unique "Memory in Cartridge" technology, is moving
tape from backup into mainstream storage.
It all adds up to an exciting year in the normally sedate world of
tape storage. End users can harness these advances to tackle their
ever-larger storage challenges.
One of the most fundamental jobs of an information systems manager is
preparing and maintaining a backup schedule for all the computer systems
under his or her care. On the surface, tape backup is a simple process.
Copy everything on a system to tape. In today's document management and
imaging systems, however, backup is becoming increasingly complex.
One of the factors complicating the backup process is the low cost of
hard drive storage. Inexpensive hard disks encourage information system
managers to buy increasingly larger RAID systems. The challenge in
backing these larger systems up on tape is not capacity. The real
challenge is speed. Larger RAID systems (100 gigabytes and up) simply
take too long to back up on tape. The speed of a drive will determine
whether a system backup will be done by the time your coworkers come in
the next morning.
One solution for the speed problem is found in tape array technology.
Just as RAID can be used to speed up hard drive access, redundant arrays
of independent tapes (RAIT) can be used to accelerate tape backups. RAIT
also better matches tape performance to the disk arrays being backed up.
Tape arrays give you the option of making a parity tape or tape mirroring
for extra reliability.
Users have a lot of options in configuring a RAIT system. It can be
single-channel SCSI or multichannel. All RAID levels are available on
RAIT systems as well. However, since tape systems are primarily designed
for maximum throughput for fast backups, RAIT systems generally don't
have to have high transaction rates. Therefore, RAID Level 3 is the best
choice for tape arrays.
A number of companies offer tape array controllers and equipment.
Ultera Systems (Laguna Hills, CA 714-367-8800) makes tape array
controllers like the Striper2 ($4,300-$4,600), a multichannel unit that
will operate two to four high-end DLT or AIT tape drives in an array.
Complete tape arrays are also available. The Superflex AIT array
($19,500-$32,000) from Artecon (Milpitas, CA 408-894-1331) comes
complete with four or seven AIT tape drives in a single enclosure.
Artecon also builds arrays into tape libraries. The P1000 Library Array
($24,000-$63,000) combines the features of a DLT tape library with a two-
or four-drive array.
Exabyte (Boulder, CO 303-442-43336) stresses matching tape
drive performance to disc performance. If you buy a tape system that's
too fast for your disc storage, you're spending money on performance
you'll never use. You also lose tape capacity as the fast tape drive
stops when it runs out of data and then has to reposition the tape to
restart recording.
If you have a fast RAID system to back up, a fast tape drive or tape
array is appropriate. If you have a large number of single hard drives to
back up, it may be more appropriate to use a number of less expensive
low-end tape drives.
You should also consider tape drive reliability. "In general, helical
scan drives have more reliability problems simply because they have more
complex mechanisms," says Myron Coppock, President of DAT
Technologies (Santa Ana, CA 949-833-2092), a company that specializes
in repairing tape and optical drives. "That holds true for all helical
scan drives, including DDS, Exabyte's Mammoth and AIT."
Despite higher repair rates on helical equipment, Coppock himself
recommends AIT drives, a helical format, citing advanced features such as
memory in cartridge (MIC) technology.
As for which tapes to use, Coppock has no opinion on the superiority
of one tape manufacturer over another. "We've found the tapes recommended
by the drive manufacturers work the best."
Introduced about a year and a half ago, Sony's (San Jose, CA
408-955-4165) AIT is a relative newcomer to the tape market. It
incorporates advanced features such as upgradeable firmware and Memory in
Cartridge (MIC).
Upgradeable firmware lets Sony make improvements on drives already in
the field. At this writing, Sony was days away from an August
introduction of a longer AIT tape storing 35 gigabytes -- 40 percent more
capacity than the previous standard of 25 gigabytes. To support the new
tape, all the drives need is a firmware upgrade.
Sony's MIC technology embeds a Flash RAM chip in the tape cartridge.
The chip stores the tape's directory, backup history, serial number and
other useful information. Most importantly, the chip allows tapes to be
partitioned into two or more volumes. If one volume on a tape goes bad,
the other volumes may still be readable. This capability will be
especially valuable as tape capacities climb above the 100 gigabyte
point, as several are expected to next year.
Another advantage of MIC is that tapes mount faster. A computer can
quickly download the tape's entire directory structure without having to
first rewind the tape or go to an online database of tape contents. This
saves wear and tear on the tapes and on the tape drive mechanism. To take
full advantage of MIC, tape management software has to be enhanced to
support the extra features. Although Sony couldn't specify which software
developers are working on MIC support, they claim improved support is
forthcoming.
MIC is so compelling, manufacturers of other tape technologies are
planning to add it to their products. Britt Terry, product manager at
Spectralogic (Boulder, CO 303-449-6400), makers of 8mm, AIT and
Travan libraries, reports that nearly all competing tape technologies --
from Exabyte and Quantum, to the IBM, HP and Seagate's planned Linear
Tape Open -- are expected to incorporate it.
"When the [drive manufacturers] all incorporate MIC, you can be sure
the [tape management] software developers will support MIC in their
products."
AIT stands alone as the capacity champ among tape drives, according to
John Woelbern, Sony's marketing manager for tape products. "AIT is
designed to combine large capacity with fast access to data," Woelbern
says.
While DLT is the throughput champ at 5 Mbyte per second, AIT matches
it in capacity (at 35 gigabytes) and surpasses it in access times, due to
its two-reel design and MIC technology.
Throughput is defined simply as the speed at which data is put on
tape. The faster the tape is threaded through the drive and the more
tightly data is packed on the tape, the higher the throughput. Access
time is an expression of how long it takes to reach a particular file on
a tape. Access time for hard disc drives is measured in milliseconds.
Access time for tape is several orders of magnitude longer and is
measured in seconds or even minutes. Tape drives like Mammoth and MLR
have access times of about a minute. AIT cuts that access time by about
half.
Tape library manufacturers are enthusiastic about MIC's fast access
speeds. "MIC allows our tape libraries to be used in place of optical
drives in COLD systems," says Bob Covey, vice president of marketing and
OEM sales at Qualstar (Los Angeles, CA 818-592-0061). "While tape
will never be as fast as disc, AIT with MIC support is fast enough for
many applications, and it will let tape be used for more than just
back-up."
Covey says "computer output to storage" will give end users greater
flexibility and lower costs in selecting storage.
AIT is catching on with tape drive manufacturers too. Seagate
(Costa Mesa, CA 405-936-1210) makes an AIT drive named the Sidewinder 50
($3,000). Named after the compressed capacity of 50 gigabytes, the
Sidewinder 50 uses MIC technology to create up to 256 partitions on a
single tape. Seagate sells the drive to tape library manufacturers and it
also makes its own AIT autoloader, the Sidewinder 200 ($6,100), which
holds up to four tape cartridges
Also known as DAT, DDS has grown into one of the most popular tape
storage solutions for desktop computers, workstations and small servers.
Recent data indicates more than 1.6 million DDS drives will be sold this
year. The popularity stems from the fact that several major
manufacturers, including Sony, Hewlett-Packard and Aiwa, have committed
to supporting the DDS standard for the long term.
Although DDS was introduced more than ten years ago (based on the
design of the digital audio tape), it is only in the last four or five
years that manufacturers have dramatically increased the format's
capacity and speed. Doug Stringer, Sony's DDS marketing manager, says it
was increased capacity and reduced cost of hard drives that spurred DDS
development.
"We try to give the tape drives at least 25% more capacity than the
hard drives commonly found in computers," Stringer explains. "With the
capacity of low-cost hard drives approaching nine gigabytes, it makes
sense that DDS-3 [the current standard] has a native capacity of 12
gigabytes."
The Digital Data Storage Manufacturers Group, which includes Sony,
Hewlett-Packard and AIWA among others, spells out DAT development through
2001. DDS-5 is expected to have 40 gigabyte native capacity per tape and
throughput speeds of up to 6 Mbytes per second.
Hewlett-Packard (Santa Clara, CA 208-344-4809) offers both
single tape drives ($1,400-$1,550) and six-tape autoloaders ($3,800 -
$4,200) in their Surestore DAT24 product line. The availability of
autoloaders has made DDS tape popular for backing up small- and
medium-sized (20-100 gigabytes) servers and networks. Hewlett-Packard
says total DDS sales will exceed 37 million drives in 1998.
DLTtape, a proprietary format from Quantum (Shrewsbury, MA
508-770-3111), is currently the speed and storage capacity champ in the
tape market. It is also the most popular technology for backing up large
systems in excess of 100 GB. A single DLT-7000 ($6,000) tape drive is
fast enough to back up a 100 gigabyte RAID system in five or six hours.
No other tape system is capable of backing up so much storage in the span
of a single night. For extra speed, DLT drives can be combined in a RAIT
system for faster throughput.
According to Mary Schoenmaker, Quantum's director of marketing, the
strategy for selling DLT is to attract users to a less-expensive
introductory drive like the 20 GB DLT-4000 ($2,500). As user needs grow,
they can upgrade to the larger and faster DLT-7000. DLT's backward
compatibility and ability to scale to very large systems makes it an easy
sell to fast-growing companies.
DLT libraries are offered by ADIC (Redmond, WA 425-881-8004),
which also makes 4mm, 8mm and AIT libraries. ADIC's $53,000 Scaler 1000
DLT library holds up to 788 tape cartridges and up to 48 drives to scale
to more than 55 terabytes.
SuperDLT is expected to debut in about 18 months with capacities in
the 100 gigabyte range and transfer speeds of about 10 megabytes per
second. Quantum is cautious about predicting the future for DLTtape, but
one thing is certain: DLT is the leader in capacity and throughput.
Shoenmaker also assures that SuperDLT, the next generation of DLT
technology, will be backward read compatible with existing DLT.
Multichannel Linear Recording (MLR) is a quarter inch cartridge (QIC)
technology developed and maintained by Tandberg Data (Simi Valley,
CA 805-579-1000). While most QIC formats are decidedly low end, MLR is a
high-end tape storage technology. Native tape capacity is currently 25
gigabytes. Tandberg boldly contends that it will double MLR's capacity
and throughput every year for at least the next three years.
MLR is also the only linear tape technology directly competitive with
helical scan tape technologies like AIT and 8mm/Mammoth. According to
Zophar Sante, Tandberg's product marketing manager, linear tape has many
advantages over helical scan tapes.
"Linear tapes have fewer moving parts because the head is fixed,"
Sante explains, adding that this translates into better reliability.
While MLR drive heads remain stationary, the head adjusts in terms of the
angle against the tape, the angle versus the direction of tape (azimuth)
and the track position. These adjustments are controlled by servo tracks
that are recorded on the tapes along with the data.
"This gives us terrific read reliability and eliminates alignment
differences between drives," Sante says.
Asked how Tandberg expects to double tape capacity every year, Sante
replies, "all we have to do is make heads with finer tracks. The amount
of data we can store is directly proportional to the number of tracks we
can get on the tape. Linear tape architecture also makes it very easy to
maintain backward compatibility."
In addition to internal and external versions of the MLR-1
($1,950-$2,150) and MLR-3 ($2,750-$2,950) drives, Tandberg sells MLR
libraries with capacities ranging from 160 gigabytes to 1 terabyte at
prices from $14,000 to $36,000.
Recently, Tandberg entered into a cross-licensing agreement with
Overland Data (San Diego, CA 619-571-5555). The deal will allow Overland
to manufacturing MLR tape drives while Tandberg will incorporate
Overland's VR2 recording technology, which will increase capacity and
throughput, into MLR-5 (2Q 1999) as well as future versions of MLR.
One of the oldest and most established tape technologies is quarter
inch cartridge (QIC) or quarter inch tape. The most current QIC
technology is Imation's (Oakdale, MN 612-704-4000) Travan. The
latest version is Travan NS20 (NS for network series). The NS drives have
SCSI connectors instead of the IDE and floppy disc interfaces common on
earlier QIC drives. They can also read and write simultaneously so the
drives can verify a tape as it's being written -- a real time saver.
Interestingly, Imation designs and sells the tapes while the drives
are made by a number of companies under license. Travan drives include
Tecmar's (Longmont, CO 303-682-3700) NS20 ($650) and Aiwa's
(Irvine, CA 949-862-0200) TD-2001 ($550).
Until recently, one of the weaknesses for Travan tapes has been a lack
of autoloaders and libraries for unattended tape backup. Autoloaders are
essential tape drive peripherals where scalability is needed. DDS drives,
Travan's principal competitor, have long been available in autoloaders,
letting you expand storage capacity along with your servers.
Spectralogic recently brought out its Treefrog Travan tape library,
giving the Travan format a scalable storage solution. The Treefrog houses
one or two drives and 15 or 30 tapes ($3,000-$8,000). A 30 tape NS20
library offers as much as 300 gigabytes uncompressed tape
storage.@IMBB:The 8 millimeter tape sold by Exabyte was one of the
original tape backup solutions available for workstations and servers.
According to Steve Georgis, Exabyte's director of technology, Exabyte has
reinvented the format with their new Mammoth tape technology.
"We're at the beginning of the product cycle," says Georgis. "Mammoth
will let us rapidly move forward with massive capacity and throughput
increases."
Indeed, the next generation of Mammoth, due by Q3 1999, is expected to
triple native storage capacity from 20 gigabytes to 60 gigabytes and
quadruple throughput from 3 Mbytes per second to 12 Mbytes per second.
"Mammoth-3 will come out in 2 1/2 years with an expected capacity of
200 gigabytes and Mammoth-4 a year and a half after that at 300
gigabytes," Georgis says. "Throughput will be up to 30 megabytes per
second and the tape drives will have ultra wide SCSI interfaces to
support that speed."
Exabyte also offers advances in hardware compression of special
interest to managers of imaging systems. Image files tend to be
compressed before they go through the backup process. In some cases,
compressed image files grow larger when put through additional
compression processes.
"The [Mammoth] compression engine can tell if the compression process
is reducing or expanding file sizes," Georgis explains. "If the
compression process expands the size of the file, the engine can turn
itself off on a file-by-file basis to keep from wasting space."
Most tape technologies available now are at the mid-point of their
development. Capacity and speed are increasing rapidly. They will
eventually run out of steam.
What's next? Hewlett-Packard, Seagate and IBM are preparing a new tape
technology expected to debut late next year called Linear Tape Open (see
sidebar, page 48). Stay tuned for news about this high-capacity format.
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