One of the more fascinating toys or objects in a grade
school science class is magnets. Give an adult two magnets, and the childhood
fascination takes over. Invariably, that person will start putting the magnets
together in attempts to make them join and repel. Many people have forgotten
the exact principle of why two magnets will attract or repel one another, but
most probably remember the experiment where iron ore on a piece of paper is made
to align one way or another. The manner in which the ore aligned itself can
best be described as longitudinal, that is, the pieces were lying down. Carry
this principle forward – and on a much smaller scale – and you have the means
by which magnetic disks (hard drives) store data.
Even on a comparatively microscopic level, each piece or bit
of information requires space on a track (at a more granular level, but still
true with respect to a disk as a whole). Looked at another way, a track has a
fixed limit for the amount of information it can contain because of the way the
bits of information are aligned. Another experiment typically performed with
the iron ore is making the fragments stand on end while passing a magnet over
them. Instead of lying down and recording, so to speak, information about the
magnetic field, imagine storing the same information by making the bits stand
on end.
Making the bits stand on end is known as perpendicular magnetic recording (PMR) technology. According to Fujitsu, its MHW2160BH model
“boasts the industry's highest storage capacity for a 5,400 rpm HDD.” In case
the significance of what a 2.5” HDD is escapes you, chances are very good that
the hard drive in your laptop or notebook computer is a 2.5” HDD. Disk drives
in the 40 to 80GB range are fairly common in OEM/out of the box laptops, so
having a hard drive with two to four times as much capacity – all the while
using the same amount of space as before – is a significant improvement.
Even more appealing is the projected increase in areal
density (number of bits per inch times the number of tracks per inch, or number
of bits per square inch of storage surface) from today’s 100 billion bits/in2
(using longitudinal magnetic recording, or LMR) to around 500 billion bits/in2
by 2010. For a perspective, consider that IBM’s RAMAC storage device (circa
1956) had a density of around 2,000 bits per square inch. Achieving the 500
billion mark is an increase of 250 million times what was available 50 years
ago. As a comparison to other advances in computing technology, this rate of
increase far exceeds rates predicted by Moore’s Law.
PMR technology in of itself is not new (considered since the
late 1970’s), but being able to apply it has been problematic because of
physics and the current state of design engineering. Engineers at Fujitsu have
overcome four major barriers in being able to apply PMR in a practical setting.
The four areas are deterioration of the bit error rate (BER) due to noise from
the soft magnetic underlayer (SUL), the wide area data erase phenomena (WATER),
the high media production cost of thick SULs, and how to obtain a low BER at a
high recording density. The advance in areal density (and making new products
cost-attractive for consumers) is indicated by the top right region in Figure
1.
To some degree, LMR and PMR are the same. Read operations essentially
apply the same technique to obtain information. The major difference is in how
data is written or stored to disk. Figure 2 illustrates the similarities and
differences between LMR and PMR.
Given that PMR is not new but that advances in design
engineering are, it would stand to reason that Fujitsu is not the only HDD
manufacturer to be in the race to product, market and sell PMR HDDs. Western
Digital announced in July 2006 that it is in volume production of an 80GB
PMR-based HDD. Hitachi has already produced HDDs based on PMR. The race is on
to push the storage envelope beyond its current limits. It is estimated that
LMR storage capacity will achieve its maximum areal density within one or two
more generations (generation meaning about one year). What is the limiting
factor driving the push to PMR drives?
The limiting factor is an effect called superparamagnetism
(the magnetic grains lose their orientation due to random thermal vibrations).
This effect will eventually limit the areal density of PMR-based drives, but
the limit is unknown at this time. Previous estimates of the top density for
LMR drives have been far exceeded due to clever design and ingenuity, and
perhaps the same will hold true for PMR drives. In any event, PMR-based drives
are currently on the market (and at reasonable prices). The “breakthrough” news
of late is of whom is releasing PMR drives when, and we can expect to hear
about areal density amounts being increased over the coming years.
How does this relate to a database? Earlier in 2006, a
Department of Veterans Affairs worker took home a laptop, which was
subsequently stolen from the employee’s house. Data about millions of veterans
was contained on the hard drive. The hard drive was probably in the 40-80GB
range in size. Imagine the implications - under similar circumstances where a
new PMR hard drive with 160GB storage capacity were in use – if hundreds of
millions of records (record = someone’s personal data) had been compromised.
Out of curiosity, what is the “take a laptop home to catch up on some work”
policy at the Social Security Administration or at the Department of Treasury
(Internal Revenue Service)?
In Closing
The underlying point of this article relates to how you should
secure your database (Oracle or otherwise). It’s not enough anymore to simply
restrict access. A portable (and removable) media storage device presents a
security challenge organizations must address. How many people in your office
carry a multi-gigabyte USB/flash drive around on a key chain? What about MP3
players? In case you didn’t realize it, MP3 players can also store any type of
file because after all, they are nothing more than miniature hard drives. The
keychain/MP3 player security threat is quite real. As our ability to store more
and more data increases, so does our responsibility to protect it.
References for Further Reading on Storage Technology
“Areal
density.” TheFreeDictionay.com. Computing dictionary.
”Fujitsu
Introduces its First 2.5" Hard Disk Drives Featuring Perpendicular
Magnetic
Recording.” Fujitsu.com. August 30, 2006. Fujitsu.
Kaitu, Isatake et al. “Ultra High
Density Perpendicular Magnetic Recording Technologies.”
FUJITSU Scientific Technical Journal, 42,1,p.122-130.
January 2006. FUJITSU.com.
“Perpendicular
Recording.” Hitachigst.com. Hitachi Global Storage Technologies.
“WD
in Volume Production of 80 GB-Per-Platter Mobile Hard Drives using
Perpendicular
Magnetic Recording Technology.” Western Digital.com. July
27, 2006. Press Releases.
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