promise of superfast access speeds has been fulfilled by solid
state drives using NAND flash memory, but it comes at a high
monetary cost. Many enthusiasts, prosumers, and corporate users have
already adopted SSDs as hard drives are typically the primary
bottlenecks in a computer system. While CPUs and RAM measure their
access speeds in nanoseconds, traditional magnetic-based hard disk
drives are still measured in milliseconds.
advantage for HDDs is the low cost of production, even for faster
7200 and 10k RPM drives. Samsung and Seagate tried before to bridge
the gap between low-cost HDDs and fast SSDs using a hybrid hard
drive, combining a single magnetic platter with a small amount of
NAND flash memory. The NAND would act as a cache, similar in theory
to a small scale tiered storage solution like that used by many
corporations for their datacenters.However, the experiment
failed. NAND was still too expensive
in 2007, and the small amount that was used proved insufficient.
Performance turned out to be worse in some situations, and the
capacity of Seagate's sole model was soon overtaken by other products
with higher areal density.
three years later, Seagate has learned its lesson with its all new
Momentus XT. The company calls it a Solid State Hybrid Drive, and it
will be available exclusively in a 2.5-inch form factor. There are
250, 320, and 500GB models, all of which feature 32MB of DRAM cache
and a 4GB single-layer cell NAND flash cache. There will
unfortunately not be any 6Gbps SATA support, despite the XT
secret sauce this time is what Seagate calls "Adaptive Memory".
The firm has developed new algorithms based on their years of
research and producing firmware for regular drives. These algorithms
monitor data access transactions over time, and will place a copy of
the most frequently accessed data (such as Windows system files) onto
flash storage. A table also keeps track and counts of how frequently
data is used in order to prioritize it for retention and caching.
is similar in concept to Microsoft's ReadyBoost, but uses much faster
SLC rather than the sluggish commodity NAND that ended up being used
flash drives and SD cards. The algorithms are also much more
advanced, as is the garbage collection and firmware. Seagate
developed its own proprietary NAND flash controller specifically for
the Momentus XT.
also means that the Momentus XT is also operating system agnostic,
and can be used with Unix/Linux environments and MacBooks.
insisted on using the flash as a cache instead of primary storage for
additional reliability. Their tests show that over 250GB of data a
day could be written to the NAND for 5 years and it would still
function.Although the Momentus XT isn't as fast as an SSD,
Seagate thinks that it will be close enough that its customers won't
be able to notice the difference qualitatively. While most consumers
will notice the difference between a 5400RPM drive and a 7200RPM
drive, they might not necessarily notice the difference between a
7200RPM and 10k RPM drive, an argument that the company has used
before as a justification for not producing a 10k RPM consumer
drive.To continue the example, Seagate likens the Momentus XT
to a 7200RPM drive and SSDs as 10k RPM drives; while the SSDs are
much faster, qualitatively consumers won't notice the difference. The
company expects that it will be able to hold off the SSD onslaught
for a couple of years with this strategy, despite the lowering
cost of NAND flash memory. In fact, as NAND flash prices drop due
to the introduction of new process nodes, Seagate will be able to fit
more NAND into the same space and offer even greater
performance.The first OEM to adopt the Momentus XT will be
ASUS for their ROG G73JH gaming laptop, which will feature two of the
drives. Seagate will also be shipping Momentus XT drives out to the
channel this week for retail distribution.Two reviews of the new Momentus XT can be found here and here.