UDO vs. DVD
The use of DVD for long-term archival storage has grown in popularity over
the last few years. Certainly Plasmon has seen an increase in sales for our own
D-Series DVD libraries within enterprise storage environments. The popularity of
DVD is based on two primary factors, low cost and format familiarity.
DVD drives and media are very low cost when compared to 5.25 inch optical and
tape technologies. While this can be a distinct advantage, there are definite
trade-offs that must be factored in when considering the total cost of operation
and ownership when compared to UDO.
A less tangible element to DVDs success is the general comfort level that
people have with the media. DVD is something that most of us have in our home.
We use DVDs daily in consumer video applications and are very comfortable with
the performance they provide. Here too, it’s important to consider the use of
this very popular consumer format in a more demanding archival storage role.
While DVD clearly has it’s place as a data storage format, increasingly
Plasmon is seeing those customers reconsider their use of DVD if they’re
operating in a demanding storage environment. Listed below are some of the key
points that should be considered when comparing UDO and DVD technologies for
long-term archival storage.
Target Market
DVD products have been designed to hit a price / performance point acceptable
by the consumer market. As a result, drives have duty cycles that are 10x lower
than UDO with read write performance that’s adequate for desktop applications,
but may not meet expectations in environments where performance is a critical
requirement.
It’s a fact that DVD drives will need to be replaced more frequently than
technologies such as UDO that were built specifically for professional
applications. The increased maintenance and replacement costs must be factored
into longer term total cost of ownership considerations. In simple terms, DVD is
a consumer technology adopted for professional use and this will have an impact
on the overall dependability of the entire solution.
Media Form Factor
Today, DVD used in libraries is mainly delivered as a bare, non-cartridged,
media which presents a significant risk to data in high duty cycle professional
environments. The handling of DVD media puts it at risk of contamination or
damage, which could result in the inability to access data. Even within a
library where the physical handling of media is kept to a minimum, there is
still a risk of contamination or damage. Customers using DVD in a production
environment should develop operational strategies that minimize the handling of
bare DVD media and may consider making redundant copies of media to be stored
off-line in the event of media damage. These types of considerations do not come
into play with cartridged UDO optical media.
Media Quality
Due to the success of DVD on the computer desktop, dozens of DVD media
production facilities have sprung up all over the world. Competition for DVD
media sales is very intense; driving down cost and quality. In addition to
quality concerns, some DVD media has been optimized to operate with specific
drive manufacturers making the media inappropriate for other drive types.
Plasmon has tested DVD media from many manufacturers and has found a startling
range in quality and compatibility.
For the storage of critical business information, it’s vital that top quality
media be used even if this means paying more. It’s tempting for customers to
select the cheapest media, but since all media is not created equally, saving a
few dollars may compromise the integrity of their data.
By contrast, products designed for the professional storage market like UDO
are influenced much less by dramatic market fluctuations. Media pricing is much
more consistent and quality from all the manufacturers is maintained at a high
level and compatibility regularly reviewed.
Recording Formats
Even before DVD was available, it was a battleground for competing standards.
Today there is a wide range of possible formats from a host of industry
consortiums each fighting for their share of the royalty pie. These different
standards have generated a good deal of confusion in the market and created
significant technical compatibility issues for hardware and software vendors.
Thankfully, two primary standards have emerged as the leading contenders for
DVD data storage: DVD-RAM and DVD-R. With the help of multifunction drives that
support multiple formats, the issues of compatibility are less critical today.
However, since these formats do have very different performance and validation
characteristics, they must be rationalized within an overall DVD storage
strategy.
Both 5.25 inch MO and UDO were developed with broad industry consensus. Each
of these technologies has one format for media recording, eliminating any
potential for customer confusion and greatly simplifying software and hardware
support considerations.
Performance and Data Verification
The two primary DVD formats for data recording are DVD-R and DVD-RAM. DVD-R
is a write once, sequential recording format without drive based write
verification. This is very similar to CD recording. This means that you must
manually verify that the data has been correctly written to the media. If there
was an error in writing, you must start the write process over with a new piece
of media. While the overall write performance for DVD-R is fairly good, there is
significant additional overhead if the write process is to be properly verified.
DVD-R uses CLV (Constant Linear Velocity) technology for reading and writing
data. CLV changes the speed of the motor as the head moves across the media;
spinning slower on outside tracks and faster on inside tracks to maintain a
constant data rate. CLV provides high constant transfer rates for large files,
but seek times are negatively affected since the drive rotational speed must
constantly change to accommodate random seek operations. The recording and
verification properties of DVD-R are very well suited for applications such as
video streaming where file access requirements are modest and data verification
isn’t absolutely critical.
DVD-RAM is a rewritable format specifically designed for data storage. It
uses a 32k hard sectored based media with 2k emulation and full write
verification. DVD-RAM drives operate with CAV (Constant Angular Velocity)
technology. CAV maintains the drive motor at a constant speed; allowing the
transfer rate to vary from inside to outside tracks. CAV provides quick seek
times, but read/write performance varies across the media surface.
When recording on DVD-R media you must first collect the target data on the hard
disk until you’re ready to burn the entire disk capacity (4.7GB). In some
environments, this can create data integrity concerns since the data must sit on
a hard disk for some time before being committed to the media. In theory, DVD-R
media can be written in smaller data packets, but in practice this “packet
writing” feature has typically not been implemented by software vendors in
library environments.
Overall, Plasmon recommends the use of DVD-RAM media with a hardcoat for data
storage since it’s the only DVD format that offers write verification. However,
DVD-RAM is a rewritable media, so some customers still prefer to use DVD-R where
write once media is important for audit trail management.
By contrast, both MO and UDO media provide dynamic write operations with full
write verification. UDO provides superior performance to DVD, greater
flexibility and a level of write verification essential to enterprise storage
environments.
DVD media is currently available with 9.4GB media capacity. Limitations with
current drive technology means that this capacity will not increase until a new
generation of Blue Laser based drives are available. While development work is
underway by several manufacturers, it may be years before next generation DVD
products are available and it’s likely that these products will be optimized for
consumer based applications and not data storage (as we’ve seen in the past).
Unlike UDO, a multiple generation roadmap for Blu-ray DVD is unclear.
Assuming product development will be driven largely by the demands of the
consumer market, it’s impossible to say whether the media capacity will increase
in line with the demands of the data storage market. If not, the product will
rapidly fall behind on capacity, performance and TCO. To date, there are no
published roadmaps for Blu-ray DVD products.
Future Compatibility
While next generation Blu-ray DVD media may well offer higher capacities,
this increased data density makes the media much more susceptible to
contamination. For this reason, it’s almost certain that next generation DVD
media will need to be delivered in a cartridge to minimize exposure to dust and
dirt. What this cartridge looks like is not yet defined and there may be
different formats from different manufacturers. This changing media form factor
means that customers with existing DVD libraries (regardless of manufacturer)
will not be able to support the new media and it remains to be seen which
cartridge form factors will be supported by which library manufacturers.
Future media form factor compatibility for UDO is not in question. UDO uses
that same ISO standard cartridge format as pervious generations of 5.25 inch MO.
Through mixed media library configurations, customers can upgrade their existing
G-Series Plasmon libraries and protect their initial library investment.
Summary Today
DVD media has a definite place within the data storage hierarchy, but like
all technologies it’s strengths and weaknesses must be carefully considered. DVD
has fitted in data storage environments where cost is an important
consideration, performance is not a driving factor and concerns about data and
media integrity are less critical or can be effectively addressed. DVD can also
be an excellent solution where media distribution or transportability is
required since DVD drives are commonly available. With the introduction of UDO,
which has specifically been designed to be a professional, permanent and cost
effective solution, the cost argument for DVD will be diminished. UDO offers a
very cost competitive alternative to DVD where performance, data integrity and
hardware reliability is critical to the archival storage environment.
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