Optical
Technology
Optical technology encompasses a
variety of media such as MO, CD, and DVD. At the simplest
level, the definition of optical systems are any devices
which incorporate a laser or use light to read or write
data to and from media. MO is simply an abbreviation
for magneto-optical as it combines both the technology
of magnetic disks (removable drives) and a laser (the
optical part), to read & write to disks.
For
the sake of simplicity however, the use of the term
'optical' is usually taken as referring to MO technology
rather than other variations such as CD or DVD which
also use laser technology. Aside from obvious differences
such as media type, fundamentally CD and DVD systems
use lasers to both read and write to their media.
Optical disks typically have faster access times but
relatively low data transfer rates compared to fixed
storage systems, but are cheaper per megabyte than hard
disks. This places them squarely in the near-line archival
sector where they are ideal under HSM (Hierarchical
Storage Management) solutions. Robotic or jukebox optical
systems can provide cost-effective high volume data
centres for less commonly-used data. Automating large
volumes in this manner also reduces management overhead.
What is an Optical
drive?
Simplistically, a MO or optical drive
is simply a storage device used primarily for data archival
and near on-line storage. As such, MO drives are ideally
suited for inclusion in library systems. MO combines
a magnetic field and an optical laser to read and write
data. On a write session, the laser reads ahead, studying
the layout of the disk to be written to, and prepares
the write head.
The
write head itself operates in a similar fashion to all
magnetic drives: it writes data to the disk by using
an electromagnetic field. The main difference between
normal magnetic drives and optical drives comes in the
read process. When data is being read from the disk,
the magnetic write head becomes redundant and only the
laser is used. This combination of optical and magnetic
technology produces a faster drive than a single technology
drive.
The
laser read process also means that the wear that is
normal associated with electromagnetic drives is reduced,
therefore improving both the reliability and integrity
of the data, together with a longer lifetime. This has
made MO technology a popular choice for data archives.
Magneto-optical disks are plastic or glass disks coated
with a compound that has special properties. The disk
is read by shining a low-intensity laser (originally
infrared - though the shorter the wavelength the higher
the possible density) onto the media and examining the
polarisation of the reflected light.
To
write, a higher-intensity laser is used to heat the
material up to its Curie
point, where it becomes susceptible to a magnetic
field. When the media cools again, its state is "frozen".
The polarity of the reflected light during a read depends
on the polarity of the magnetic field under which the
media was last cooled. Once it has cooled it is no longer
susceptible to magnetic fields.
How many times can you rewrite
data to the same disk?
According to Sony's engineers the figure
is extremely high. They place a figure of around 10
millions times per disk. This high write figure is based
upon the simple fact that in magneto optical drives
the heads never the touch the disk, so there is no physical
deterioration that can affect the data.
How long can the data be stored on the disk?
Data may be stored with magneto optical
technology for more than thirty years without loss or
degradation. Once written to the disk, data is safe
from the magnetic fields and heat found in normal environments.
If
you need to ensure the security of data slated for long-term
archival storage, consider media that is classified
as Write Once and Read Many (WORM), such as Sony's 5.25-inch
MO media. HP also embrace WORM classification for secure
long term archiving. This media protects valuable data
from ever being overwritten, and has in essence, the
opposite advantages from LIM-DOW technology. In fact,
HP do not subscribe to LIM-DOW technology as they state
that the technology is too immature and untested for
critical data archival solutions.
What
applications do high capacity media such as MO storage
benefit? |
MO
is ideal for capacity-intensive applications that
require fast data transfer, near on-line access,
and rewritable or write-once backup/restore at a
cost-effective price. |
Application
areas include:
- Audio/Video
Editing
- Document
Imaging
- Graphic
Design
- Desktop
Publishing
- Document
Filing
- CAD/CAM
Engineering
- Industrial
Design
- Prepress
- Medical
Imaging
- Digital
Video
- Multimedia
- Accounting
- Banking/Finance
- Law
|
HP Optical Library
|
So
if your hard drive is filling up or the security
of your data is extremely important, an archival
library built on MO media is an excellent solution.
Many solutions such as Computer Associates HSM (Cheyenne
HSM as it was previously known) insists on the secondary
HSM storage stage being comprised on MO systems.
Archiving logic dictates that MO data is migrated
to tape as it reaches access and back-up thresholds.
This places MO robotic systems such as jukeboxes
firmly between hard drive or other fast access fixed-block
storage systems and the inexpensive, high capacity,
but much slower technology of digital tape systems.
|
HSM
- MO & Tape Implementations
MO Libraries are ideally suitable for
use in HSM environments as Secondary Stage migration destinations.
For comparable Tertiary Stage HSM destinations, large
Tape Libraries or Autochangers can be ideally implemented.
As these tape systems can also be doubled for back-up
purposes, the implementation costs can be quickly recouped. |