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War of the Disks: A Close-in Analysis
of the
Hard Disk Drive vs. the Solid State Disk
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Mortality Rate
Hard disk failure is a common occurrence in this age of desktops
and notebooks. A lot of horror stories have been told, passed around
and even published about how valuable data was lost and the agony
of trying to retrieve or at least save a portion of the crashed
hard drive. It is during this time that people wonder, why do hard
disks fail?
The reason is simple - wear and tear. Just like any good old machine
with mechanical components, HDDs tend to deteriorate over time.
HDDs consist of rotating, magnetically coated disks, known as platters,
that are used to store data. This rotating motion of the mechanical
arms results in much wear and tear after long periods of use. The
operational lifespan of a computer HDD is over three years .4
A Flash-based SSD is different. Although the most common Flash chips
have around 300,000 write cycles, the best Flash chips are rated
at 1,000,000 write cycles per block. On top of that, Flash SSD manufacturers
employ different ways to increase the longevity of the drives. In
some cases, they use a "balancing" algorithm to monitor the number
of times each disk block has been written, which greatly extends
the operational lifespan of the drive. Furthermore, these manufacturers
also designed special "wear-leveling" algorithms where once a certain
percentage threshold for a given block is reached, the SSD will
swap the data in that block with the data in another block that
has exhibited a "read-only-like" characteristic in the background.
This reduces performance lag and avoids further wearing off of the
blocks and thrashing of the disk. Even with usage patterns of writing/reading
gigabytes per day, a Flash-based SSD should last several years,
depending on its capacity. Add to that the inclusion of a DRAM cache
in the disk architecture that further enhances its operational capabilities
as well as lifespan.
Speeding Up
With the very fast paced lifestyle these days, most businesses are
time-bound and cannot afford a slowing down in their transactions.
This makes speed of HDDs a crucial point in technological purchases.
The typical access time for a Flash based SSD is about 35 - 100
s, whereas that of a rotating disk is around 5,000 - 10,000 s. That
makes a Flash-based SSD approximately 100 times faster than a rotating
disk.
This however raises another point - what's the benefit of a high-speed
SSD when the entire system cannot support it? The evolution of CPUs
in terms of performance has far surpassed the development of the
data storage system. The HDD is actually limiting the potential
of a computer system when they are not able to keep up with the
performance of the other components, particularly the CPU. If an
HDD is replaced by a high-speed SSD, the performance would significantly
improve. The resulting system would be a high-powered set-up that
can go beyond the demands of high-speed business or military environments.
Size Matters
To be a true plug-in replacement for HDDs, Flash-based SSDs are
manufactured in standard 2.5" and 3.5" form factors. 2.5" SSDs are
normally used in laptops or notebooks while the 3.5" form factors
are used in desktops, or in JBOD or other SAN/NAS/DAS configurations.
They can often be used to replace traditional disks in storage arrays
or in a server's internal disk bays. Flash-based SSDs certainly
fit the storage needs of most embedded systems that require much
smaller form factors. Reliability
In terms of reliability, conventional HDDs pale when compared to
SSDs. The absence of mechanical arms and spinning platters is the
reason behind its reliability. In demanding environments, SSDs provide
the type of ruggedness required for mobile applications. Unlike
the HDD, SSD's can withstand extreme shock and vibration with data
integrity and without any danger of data loss. This feature is very
important in industrial applications where exposure to highly combustible
materials and electromagnetic radiation are typical. Their ability
to deliver unnerving performance in extreme conditions also makes
SSD play a vital role in military operations, be it in defense,
aerospace or aviation applications. Military applications require,
in most cases, an operating temperature range of -60°C to +95°C.
Shock, vibration, and temperature ratings of HDDs cannot comply
with military standards, only SSDs can. Power Play
In addition to speed, reliability and mortality rate being positively
affected by the SSD's non-volatility, they also consume much less
power than traditional HDDs. No additional power is required to
activate the platters or the mechanical arms present in most HDDs.
Its power consumption is practically only a fraction of a hard disk
drive. Heat Dissipation
Along with the lower power consumption, there is also much lesser
heat dissipation for systems using Flash-based SSDs as their data
storage solution. This is due to the absence of heat generated from
the rotating/movable media. This certainly proves to be the one
of the main advantages of Flash-based SSDs relative to that of a
traditional HDD. With less heat dissipation, it serves as the ideal
data storage solution for mobile systems such as PDAs, notebooks,
etc. Users can do away with large cooling fans, internal power supply
and batteries for large storage arrays in storage area networks.
Cost Considerations
Of course, everything comes with a price. Based on a cost-benefit
logic, it is but expected that something with very impressive features
be priced higher than something that offers fewer benefits. SSDs
as being a bit more pricey than the traditional hard disk drive
may be one of the compelling reasons why up to now it hasn't gained
as much popularity as it should be getting with all its brilliant
functions.
While the use of SSDs today have mostly been limited to industrial
and military implications, enterprise are now looking closely at
SSDs for implementing tiered storage and optimizing their storage
architectures.
To quote from the Solid State Disks Buyers Guide published by storagesearch.com,
"In fact the SSD is replacing servers and software licenses. SSDs
can be used either to speed up the response time of existing applications
as an alternative to buying more servers, or to reduce the number
of servers and software licenses deployed. The economics can be
compellingly in favor of an SSD deployment". The industry is also
expecting more breakthroughs as higher memory capacities and faster
performance are now being produced for a wider array of choices
fit for any mission-critical application.
Analysts foresee a rapidly closing gap between HDD and flash SSD
pricing (see related article "Are Flash Solid-State Disks Ready
for the Enterprise"5 ). This vision is also bolstered
by a recent announcement6 of electronic giant Samsung
that they will invest heavily in improving their flash and DRAM
production lines and flash SSD equipped laptops. Only time will
tell if we will witness widespread commercial adoption of SSDs.
4Source: http://www.cmu.edu/corporate/news/2004/0604_critter.html
5Source: http://www.bitmicro.com/press_resources_flash_ssd_enterprise.php
6Source: http://www.techworld.com/storage/news/index.cfm?NewsID=3967&email
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