MESSAGE
| DATE | 2013-04-05 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] The New Hybrids ....
|
http://techreport.com/review/24561/seagate-laptop-thin-sshd-500gb-hybrid-drive-reviewed
What do the McLaren P1, the Porsche 918, and the Ferrari LaFerrari all
have in common? They're limited-edition supercars with price tags well
out of reach for mere mortals. Also, they're all hybrids. Even in the
world of high-end exotics, internal combustion engines are being paired
with electric motors.
Right now, hybrids seem likely to be the next evolutionary step for
automobiles. Their electric motors are both efficient and
environmentally friendly, while their fuel-based engines provide the
road-trip range people have come to expect. There's a similar parallel
in the PC storage industry.
Modern SSDs are much faster than traditional hard drives, but even with
Moore's Law chipping away at NAND prices, they remain relatively
expensive if you want loads of storage. SSDs in the 240-256GB range
typically cost around $200, and they still don't give you a lot of
space, especially if your media library is going to share the drive with
your OS, applications, games, and other data.
While mechanical hard drives can't keep up with the performance of SSDs,
their spinning platters can store a lot more data per dollar. Marrying
the two in a hybrid configuration is a no-brainer, and it's incredibly
easy to do in desktop systems that can accept multiple drives.
Notebooks, however, are a whole other animal. Some laptops permit
mechanical drives to ride shotgun alongside mini mSATA SSDs, but most
are limited to a single drive.
Since mid-2010, Seagate's solution for single-drive notebooks has been
the Momentus XT, a hybrid that combines flash memory and mechanical
platters in one 2.5" chassis. The original model and its
second-generation successor have had some appeal, but they've been
hampered by read-only flash caches that ignore incoming writes from the
host. That limitation has been lifted in Seagate's latest hybrids, which
can cache both read and write requests.
The first of this new generation to hit our labs is the Laptop Thin SSHD
500GB. (SSHD stands for solid-state hybrid drive, in case you're
wondering.) Although painfully generic, the model name gets the point
across. This is a laptop drive with a thin form factor and 500GB of
storage. And it's eminently affordable, with a street price hovering
around 80 bucks. Naturally, we had to take a closer look.
Thin is in
Most 2.5" hard drives are 9.5 mm thick, but the Laptop Thin SSHD
squeezes its guts inside a 7-mm case. This thinner chassis is a better
fit for the growing field of super-slim notebooks spawned by Intel's
ultrabook initiative. It also represents a first for Seagate's hybrids,
which have previously been limited to 9.5-mm models.
The 9.5-mm Momentus XT (left) next to its Laptop Thin sibling (right)
To help its hybrid diet down to the smaller form factor, Seagate removed
one of the platters. The Thin Laptop SSHD has a single disc with a 500GB
capacity. Bits are packed with an areal density of 705Gb/in², which
allows each side of the platter to store 250GB. That bit density is 30%
higher than that of the old Momentus XT 750GB, whose dual platters pack
541Gb/in².
An increase in areal density usually leads to better performance for
sequential transfers. The more bits per square inch, the more data
passes under the drive head with each revolution of the platter. On the
Laptop Thin SSHD, however, there is one rather significant catch. The
platter spins at only 5,400 RPM—25% slower than the Momentus XT's
7,200-RPM spindle speed. This slower rotational speed negates much of
the advantage of the increased bit density.
Seagate contends that spindle speed is less important for hybrid drives,
and the benchmark results later in this review will shed some light on
that claim. The firm is certainly confident, because it's committed to
stop making 7,200-RPM notebook drives altogether. 5,400-RPM hybrids will
replace high-speed drives in Seagate's notebook lineup, allowing the
company to focus development on a single mechanical platform for mobile
PCs. That platform will presumably be shared by SSHDs, notebook hard
drives, and external storage products.
We tend to recommend 5,400-RPM drives only when they're being paired
with SSDs, which is essentially what's happening here. In addition to
500GB of mechanical storage, the Laptop Thin SSHD has 8GB of flash
memory. Like in previous Seagate hybrids, the flash is governed by a
caching mechanism dubbed Adaptive Memory. This scheme categorizes data
based on two criteria: how frequently it's accessed and whether
relocating it to the flash will improve performance. Solid-state storage
is orders of magnitude faster than mechanical storage for random
accesses, but the two are more evenly matched when data is accessed
sequentially.
Adaptive Memory can see precisely how data is organized on the disk, a
level of insight absent from software-based caching mechanisms like
Intel's Smart Response Technology. According to Seagate, this low-level
visibility allows its hybrids to make better decisions about what to put
in the flash. Because the caching magic works entirely within the drive,
the Laptop Thin SSHD requires no drivers or software. It'll work with
any operating system and hardware platform.
Folks familiar with hybrid storage will note than the Laptop Thin SSHD's
8GB flash cache is relatively small. The NAND footprint hasn't grown
since the last Momentus XT, which is a particular concern given the new
model's ability to cache data for writes in addition to reads. Product
manager David Burks told us Seagate experimented with different cache
sizes and found that 8GB was big enough for mass-market workloads. The
data access profiles of typical consumer and commercial workloads don't
change dramatically, he said.
Seagate hasn't revealed many details on exactly how the write caching
mechanism works, but Burks confirmed that data is prioritized in much
the same manner that it is for reads. Whether an incoming write can be
processed faster by the flash plays a role in determining whether it
will be cached there. We haven't heard back from Seagate on how much of
the flash is reserved for incoming writes and whether the distribution
is static or dynamic. Burks did, however, tell us that the drive has
enough onboard capacitance to ensure that the contents of its write
cache can be written to the disk in the event of unexpected power loss.
|
|
