Magneto-Optical Storage comes of age
Magneto-Optical Storage comes of age
By Zatni Arbi
JAKARTA (JP): The 5.25" rewritable magneto-optical (MO) disk
was a hot, newly-released storage product in 1988. But for four
years following its launch its storage capacity remained static;
at 650 MB of data. In the last few years there has been a
dramatic change, however, and we now have MO disks that hold up
to 1.3 Gigabytes of data on two sides (650 MB per side). Some MO
disks can even store 2.6 'Gigs'. We now also have the 3.5", 128
MB version of the MO drives and disks.
Pinnacle Micro, from Irvine, California -- one of the major
players in MO disk storage -- released its interesting Orray
optical disk system last year. Partly following the model of the
hard disk-based RAID storage architecture, Orray has four
removable 1.3 disks in one casing, allowing you to store up to
5.2 GB with the speed of a hard disk. That was a boon to MO
enthusiasts, as this technology had traditionally been known for
its slower disk access times and longer disk write times when
compared to magnetic hard disks. Unfortunately, at almost
US$15,000 per unit, the Orray system was out of many people's
reach.
Much less expensive than Orray -- but still expensive for
ordinary applications -- are the MO drives from Sony. I was lucky
enough to be able to test drive Sony's 5.25" MO drive, the SMO-
F521, which carries a Rp 4.5 million price tag.
Magneto optical
I had been searching the mass storage market for a database
for my office. To begin with, we wanted to build a simple
database to meet the needs of our administrative department. In
time, though, we wanted to develop the system into a fully-
fledged database, supporting the work of our researchers as well.
Given this growth consideration, I set out to find a better
alternative to a high-capacity hard disk with a tape backup
system -- the traditional means of storage for databases.
Definitely, the storage system I was looking for would allow
plenty of room for growth.
Among the products available in Glodok, Jakarta, are the
double-density MO drives from Sony. The internal drive that I
tested looked almost like a regular CD ROM drive, except that it
was more than one inch deeper and was much, much heavier because
of the complex optical mechanism contained in it. For fear of
scratching the sides of the loaned drive, I never tried to slide
it into my PC, but it should fit into any 5.25" bay without
difficulty. Of course, if you happen to have a mini tower or a
slim case, you will probably run into a space problem.
Other MO drives from Sony that are available in Glodok include
the 5.25" external and the 3.5" internal (the latter stores a
maximum of only 128 MB per disk). The one I tested was an
Original Equipment Manufacturer (OEM) version, which means that
there is no Sony logo on the front panel. You can find both the
unit I tested and its external cousin in the accompanying
illustration. The price difference between the Sony brand and an
OEM unit is pretty substantial, at about Rp 1 million.
I tested this MO drive with a SCSI-2 board from AdvanSys,
i.e., AdvanSCSI Silver Multi-media Kit. I've chosen the ISA bus
master version of this SCSI board, as I still don't know whether
it will be used on a VL or PCI PC (while the speed is not
optimal, the ISA board gives me the freedom to choose the system
to install it later on, as it can be used on both VL Bus and PCI
motherboards). AdvanSCSI comes with CorelSCSI-2 software and a
ribbon cable for internal SCSI devices.
Using the universal Write-Once/Rewritable driver that comes
with CorelSCSI, I was able to add the MO drive to my system. I
haven't been fully successful in setting up the SCSI subsystem
correctly, as Central Point Backup still doesn't recognize it.
Nevertheless, the MO drive became Drive D: while my regular CD
ROM drive became Drive E:. I was able to write on the MO disk and
read from it with no problems.
MO Basics
In an MO drive, the data recording, reading and erasing
operations rely on the use of an electromagnetic head, a laser
diode, two polarized beam splitters, and two photodetectors --
one for "0"s and the other for "1"s. The recording layer of the
disk contains magnetic domains, the orientation of which can be
changed during the recording operation with the help of the heat
from the laser beam and the application of an electromagnetic
field (it's a combination of thermal and magnetic recording
mechanisms). When the magnetization is upward, it is a "0"; when
it is downward, it is a '1".
During the read operation, the direction of the magnetic field
affects the direction of the reflected laser beam, and using the
so-called Kerr Effect calculation the read mechanism will
determine whether it is reading a "0" or a "1".
Sony claims that the average seek time is 40 ms, and the data
transfer rates are 2.0 MB/sec or 1.0 MB/sec, depending on whether
the data is stored on the outer or inner ring of the disk
platter. Needless to say, this level of performance is still far
below an SCSI hard disk, although it is far better than the
floppy disk or tape.
MO Cartridges
For the drive, I was also able to test the 1.3 GB cartridge,
which you can see in the accompanying illustration, too. The
price was about Rp. 400,000 a piece. Actually, each side of this
cartridge stores 652 MB of data, and you can flip it to use both
sides. The DOS FORMAT command will not work with this cartridge.
However, both CorelSCSI's DOSTOOLS and WindowsTOOLS will format
it in less than three seconds.
Sony claims that, since it uses the magneto-optical system,
the disk can be rewritten a virtually unlimited number of times.
As they put it, "the error rate will not change even if the disk
is rewritten more than 10 million times".
Test results
Using the simple DOS XCOPY/S command, it took me almost three
hours to back up my nearly full 540 MB IDE hard disk to the MO
cartridge. Using CorelSCSI Backup utility took almost as long.
But this extended backup time could have been the result of a
less-than-proper SCSI setup, in addition to the fact that MO
drives always take longer to write than to read.
To test whether the MO was still suitable for primary storage
purposes, I installed Photoshop 3.0 on the D: drive. When I
started the program, it didn't take noticeably longer time to
load than when I started it from the hard disk. The reason for
this snappy performance is perhaps that Photoshop is a memory-
intensive rather than disk-intensive program. Frankly speaking,
as I'm a true beginner in Photoshop I don't know how to test the
drive to its limits with this top graphics program. Nonetheless,
I noticed that it didn't take very long to load the many sample
images that came with Photoshop 3.0.
I then tried to run Calligari's TrueSpace, a high-end 3-D
animation program, from its backup directory in drive D:. The
program still ran acceptably fast, so I think it's safe to
conclude that you can run your programs -- if you don't have a
better choice -- from an MO drive, albeit perhaps at a 386
performance.
Unfortunately, I didn't have a large database to test the
performance of MO. A huge database would have been the best tool
for this kind of test, as applications such as this one are much
more hard-disk intensive. In general, however, MO disks are
considered suitable for applications such as archival storage,
document management, image processing, and large-sized databases.
Conclusion
Let's do some straightforward maths here. If we buy an MO
drive and a cartridge, both will cost us Rp4.9 million and both
will give us a 1.3 GB storage space. That means that the MO
system will cost about Rp. 3,750 per MB. That doesn't sound very
enticing, given the current price of high-capacity SCSI hard
disks, of Rp 1,400 per MB. However, as we add more cartridges,
each of which comes at Rp 300 per MB, the MO option becomes more
attractive. While the initial investment is hefty, the price per
MB storage capacity becomes cheaper as its total size increases.
Add to this expandability the benefits that hard drives don't
offer, such as portability, durability (the cartridge is backed
by a five-year warranty), longevity (Sony claims it to be at
least 15 years), and security (you can easily keep a cartridge
containing sensitive data in a safe place) and, depending on your
requirements, MO may prove an excellent alternative for mass
storage.