TAPE OR DISK STORAGE? MAYBE BOTH
From: Dr. Jai Maharaj (usenet_at_mantra.com)
Date: 09/21/04
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Date: Tue, 21 Sep 2004 23:09:15 GMT
Tape or disk storage? Maybe both
The choice of enterprise storage systems
may not be as clear-cut as champions of
disk systems might suggest.
By By Anand Parthasarathy
The Hindu
Thursday, September 16, 2004
WHEN THEY speak of 'incumbency factor' in Indian
politics, it usually means the guys in power tend to be
thrown out, the next time the electorate gets to decide.
In the world of computer storage, though, incumbent
technology has often exhibited the 'stickiness' required
to last longer indeed, long after experts have written it
off.
Ever since the first IBM main frame computers, fifty
years ago, used those jumbo-sized tape drives, magnetic
tape -- where different patterns of magnetisation are used
to represent stored bits or bytes of information -- has
remained the dominant media for the storage of digital
information.
Earlier technology
In the early 1980s, optical technology was born, giving
birth to the compact disk (CD). But rewriteable CDs were
costly and complicated... . the main data storage medium
of the personal computer remained the hard disk. 'Mag
Tape' however, was the preferred medium to back up and
archive data -- and tape systems have gone through many
evolutions, from the low cost DAT (Digital Audio Tape)
drives to today's DLT and SuperDLT ( Digital Linear Tape)
drives. In the DLT drive, data is written on the tape in
dozens of straight-line (linear) tracks, usually 128 or
208. A variant of DLT technology, called SuperDLT, makes
it possible to store upwards of 300 GigaBytes (GB) on a
single cartridge allowing data transfer speeds of up to
60 Giga Bits Per Second (GBPS). Competing devices include
the Linear Tape Open Drive, the Advanced Intelligent Tape
(AIT) drive, created by Sony with rated capacities
hitting 500 GB, and the Mammoth drive.
Disk costlier than tape
Meanwhile the cost per unit storage of magnetic hard disk
systems, fell dramatically -- almost by a factor of 1000
within a decade. By 2001 it overtook magneto-optical
drives -- which combined the speed and capacity of optical
technology with the flexibility and reliability of
magnetic drives -- as the cheaper medium. But within the
magnetic spectrum, disk remains costlier than tape by a
factor of five to ten. Today we talk of cost in terms of
dollars per GB and speeds of data transfer in terms of
GBPS.
Disk array systems with their much faster transfer speeds
and their ability to swiftly and non-linearly reach the
data one wanted, have captured most of the high-end of
the enterprise storage business, as the best bet for both
primary storage and secondary back up. And whether the
storage architecture is Storage Area Networks (SAN) or
Network Attached Storage (NAS), disk seems to rule as the
technology of choice. Which is why, some industry
watchers have begun polishing their obituaries for tape-
based systems.
That would be a mistake, feel leading manufacturers of
tape storage solutions who have banded themselves into
the Tape Council (www.tapecouncil.org) .
Their web resources explore the tape-versus-disk issue
from many angles and conclude that tape-AND-disk would be
a more realistic appraisal of the storage scenario today.
Last month, I had the benefit of a detailed technical
discussion with the world's largest manufacturer of the
de facto standard, the half inch (12.6 mm) DLT/SuperDLT
tape drive -- the US-based Quantum Corporation.
'Masala-mix'
Jim Simon, Quantum's Director of Marketing for Asia
Pacific explained that in today's typical enterprise, 80
per cent of all access targets just 20 percent of the
data within a storage system.
System managers therefore, try for the right 'masala mix'
of storage media -- disk and tape -- to create an
economical system. With tape systems much cheaper (albeit
slower), it makes sense to use costly disk arrays for the
most-used current data and its 'hot swap' backup,
constantly shifting the larger, more archival storage, to
economical tape.
Typically today, tape costs around $350 per terabyte
versus disk's $1500 and more. Tape, if properly
maintained at around 20 degrees C can last for at least
30 years.
Indeed, an interesting new 'cross over' technology has
emerged -- Tape Virtualization -- where a disk array is
configured to emulate a tape library. This makes it easy
to transfer each logical 'tape' in the disk array to a
real tape, once it is no longer required for critical
operations.
Quantum's India Country Manager Sunny John, added an
interesting reason why tape has suddenly assumed new
importance, particularly in India: Companies in data-
intensive industries , particularly, those doing off
shoring, are now required by law in many customer-
countries led by the U.S., to follow strict data
retention and archiving norms.
Multiple layers of security are required to achieve this
and tape players like Quantum have reacted by creating
specific solutions like DLTIce -- a write once, read many
times (WORM) tape solution -- to address this new need,
while maintaining backward compatibility with existing
DLT tape drives.
Future scenario
And in the future? They are already gearing for the day
when both tape and disk will hit the physical limits of
magnetic storage -- their areal density or the maximum
amount of data they can store per square cm.
Sometime between 2007 and 2010 the concept of holographic
data storage may take over: Light from a laser is split
into two beams, one the signal carrying data, and the
other, a reference. The two overlap inside a
photosensitive storage medium to produce an optical
interference pattern.
- Anand Parthasarathy
More at:
http://www.hindu.com/seta/2004/09/16/stories/2004091600201400.htm
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"And a man's foes shall be they of his own household.
- Matthew 10:34-36.
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