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Discovery StorageWorld - Optical Storage SolutionsClick here for Discovery StorageWorld home page
Optical Technology How long can the data be stored on the disk?
What is an Optical drive? HSM - MO & Tape Implementations
What applications does MO storage benefit?
   
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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
Optical Library
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.
 
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