Why is it that a disc drive can be bought for a couple
hundred dollars yet I have to pay thousands of dollars to get a
storage array?
Be careful about the items that you're comparing. The hard
drives used in the consumer market are not the same devices that
are used in enterprise storage
arrays. Enterprise-class hard drives are designed to offer
performance and reliability that are better than consumer-class
drives -- this drives up the cost of enterprise drives and inflates
the cost of enterprise storage arrays. For example,
SATA enterprise or desktop disc drives that have gone through
more exhaustive and time consuming testing and burn-in are also
combined with dual-porting cards for availiabity -- adding to the
cost of a drive.
But the cost of an array goes far beyond the hard drives.
Storage arrays also demand power supplies, cooling and controllers,
many of which are redundant. Software design and testing also has
to be included. And all of the design/engineering time that went
into the array has to be recaptured over time. Array vendors also
have to make a profit to stay in business and continue to invest in
research and development, sales, marketing, etc.
From a practical standpoint, you could go off and buy the drives
and other parts, write your own software/firmware and then stitch
it all together to form your own storage array, but why would you
want to unless you have a lot of free time and resources at your
disposal?
Go back to the beginning of the
Disc Hardware FAQ Guide.
How are drive power demands changing? What power-saving
features should I be looking for when selecting drives for my
storage array, and what is a sleepy disc drive?
Each new generation of drives offers better capacity and
performance but is generally using less power -- both at spin up
and during normal operation. It's important to avoid focusing on
the individual drives. For example, small form factor drives are
drawing less power but allow more drives to be packed into the same
physical area. You may find that the total power demands of your
new high-density array are greater, even though each individual
drive may use considerably less power. Several large drive arrays
already incorporate some form of drive power management at the
system level, though the most interest is in managing power
autonomously at the individual drive level, including different
power modes. Also, look at the over all effectiveness of the drives
and the storage controller to increase performance while reducing
drive power consumption as opposed to simply looking at gigabytes
of storage per unit of electrical power (watts).
Hybrid drives using substantial amounts of onboard
RAM or
flash memory to cache platter contents are
particularly interesting in terms of power management. When the
physical hard drive isn't actually needed, its contents have
already been cached to onboard memory; the drive could operate
at reduced revolutions per minute or spun down completely.
Meanwhile, the drive's data is accessed from the onboard memory.
When the needed data is not in memory, the drive is spun up and
the platters are accessed.
Still, spin-up power remains an important issue. It's possible
to spin down numerous drives and save substantial running power,
but spinning up a large number of drives simultaneously can produce
a significant surge in power demands. Frequent starts and stops may
also have an adverse effect on long-term drive reliability.
Consequently, a trend is to use multiple power modes on disc drives
to vary performance and power consumption while prolonging disc
drive use.
Go back to the beginning of the
Disc Hardware FAQ Guide.