View from the Hill:- Introducing WORM Hard Disk Driveshard drives -
with a write disable switch for specified zones
February 28, 2005
articles & news
History of Disk to Disk
Methods for Cleaning Up Hard Disk Drives
|WORM Hard Disk Drives
will be coming to the market in a year or so. Remember where you heard it first.
The same place which predicted the convergence of services, online content and
storage which became embodied as Apple's iPod and iTunes.
Words and their connotations can change their
I first heard the term "WORM" (Write Once Read Many
times) back in 1980 - used in the context of one time programmable non volatile
Back then Intel was trying to convert manufacturers to use
EPROMs (Erasable PROgrammable Memories) in low cost OTP windowless plastic
packages for production runs instead of the more expensive ceramic packages
used for development which had windows enabling the devices to be erased in a UV
light box and reused. The plastic packages also had the advantage of being
compatible with robotic insertion - unlike the more brittle ceramic.
1986 I was hearing the term "WORM" again, this time referring to the
new generation of 5.25 inch optical disk drives which were hitting the market as
long term archival storage.
Then for over a decade the terms WORM and
optical storage were synonymous, although the fashionable technology of the time
changed from writable CD, then writable DVD, and now HVD (Holographic Versatile
Then in 2003 - a new type of WORM wriggled into our
consciousness - the idea of one time writable tape backup. Introduced by Sony as
a feature in its SAIT drives - the concept seemed bizarre at first. But there
were good commercial reasons behind the idea. US laws governing the ways in
which data had to be archived created a guaranteed market for any data
archiving technology which made accidental erasure of data foolproof. Sony
managed this with some flash memory inside the tape cartridge which remembered
that it had been configured as a WORM device and prevented over-writes at the
low level driver level.
I'm going to introduce a new idea - and
remember where you heard it first. Because in a few years time this could be a
multi billion dollar segment of the hard disk drive market - which needs all the
revenue it can get - as it's under constant pressure from two main trends:-
- a capacity versus price technology curve which at
times has much in common with the type of cliff that lemmings (or venture
capitalists wedded to learning curve pricing) like to throw themselves off
My new WORM concept - which you may already have anticipated
by this point - is WORM HDDs.
- serious threat of obsolescence at the entry level
capacity end - by lower priced, lower power and more resilient flash disks.
There are many reasons why WORM HDDs will
come and are inevitable.
The main one is that if hard disk drive
technology is to become the real replacement for
tape storage - then cost
per bit competitiveness - which some vendors claim has already been established
- is not enough. HDDs will have to become available with true WORM capability -
which means they will have to include a mechanical switch which enables them to
be configured as WORM devices - and which over-rides driver level over-writes of
the files on the disk when the directory is full. (Later - some
makers now offer this feature.)
This will require
standards to be set up so
that drives from different manufacturers understand how they are supposed to
operate. That process could be managed by a current trade body like
IDEMA. Or it could be managed by a new
body set up for the purpose.
WORM HDDs will have to have some other
characteristics - such as the ability to power down - and power up by remote
control in a predictable way - otherwise the power consumption of Petabyte disk
archives will be horrendous. Some drives already do this. For WORM applications
- low cost, low power and high MTBF will be more important than high
performance. But we're already seeing many of these capabilities in newer
serially connected hard disk drives.
will hard disk drives compare to optical media or tape - when you come to read
the data off them in 5 to 10 years?
Well - tape isn't exactly
If you don't rewind and rewrite the data from time
to time it's not guaranteed to stay there. And tape media can stick and jam.
Similarly optical media is subject to aging effects. If you take the unit of a
hard disk drive WORM repository as being a network connected
RAID system rather than a
single disk drive - then the problem with long term data viability is easily
resolved. At some stage in the 5 to 20 year cycle - when it's no longer economic
to buy replacement drives - you just move the data onto another newer replicated
WORM HDD system.
WORM HHDs will have a number of advantages compared to
write many times disks. For example - the risk from viruses or administrator
error deleting large chunks of replicated data (which does already happen with
conventional RAID based disk to disk backup systems) will be eliminated. And
compared to WORM tape - the WORM HHDs will be faster to read and write.
will also have a FUD (Fear Uncertainty and Doubt) advantage compared to
newer optical storage
technologies - in being proven. It sometimes takes several years for the
long term reliability
of new storage media to be proven - and often the extrapolated data
permanence and error
rates in past technologies have been revised downwards following a few
years of actual product experience.
And finally, WORM HDDs have the
same superficial advantage that almost guarantees that the concept will be
adopted. Like Internet SCSI,
Serial Attached SCSI
and similar concepts - we're already familiar with the words.
|"The user mood is
changing from - can I afford to use SSDs? to a realization that - I can't afford
not to use SSDs."|
|where does all the money
| Would users buy an SSD
just because it has an animal printed on the label?|
If so - what
animal should it be?
|Animal brands in