18/08/2013
You’ve got SSD questions, we’ve got SSD
answers. It’s time for a crash course in
solid-state drive technology
Solid-state drives ( SSD) are taking the PC world
by storm with their silent operation, blazing
speeds, and ever-sinking prices, and yet you're
hesitant to buy one. Maybe you're afraid of
SSDs, or you don't think you know enough to
make an educated purchase, or maybe a bad
SSD controller took all your data down to
Chinatown. Regardless of the reason for your
trepidation, every horsepower ju**ie should be
getting in on the SSD action, and to do that
you need a little bit of cash and a whole lot of
knowledge. In this article, we will attempt to
answer all of your SSD-related questions. We'll
walk you through all the reasons why you need
an SSD first, then break down the terminology
so you can talk like an SSD badass at the next
LAN party, then show you the parts of an SSD
so you know how it all fits together, and we'll
wrap it up with a discussion of the software
you'll need to monitor and optimize your
drive. Though SSDs might seem complicated
with their 24nm synchronous MLC Toggle
NAND flash and their AHCI-enabled SATA 6Gb/
s IOPS gobbledygook, you're about to find out
they are not as scary as you thought they
were.
What Is an SSD and Why Should You Care?
Demonic speed and immunity to tumbles
are part of the story
Let's start with the basics. An SSD is a solid-
state drive, meaning it has no moving parts.
It's basically a thin slice of NAND flash
memory that’s similar to what you find in a
USB thumb drive, though instead of being
jammed into a finger-size stick it’s stuffed
inside a 2.5-inch enclosure with a SATA
interface. As you have probably heard, SSDs
are several orders of magnitude faster than
mechanical hard drives for one simple reason:
Instead of waiting for the hard drive platters
to spin under the read/write heads, you are
pulling data from NAND flash memory, so
access times are nearly instant. SSDs are so
fast that some of them are currently able to
completely saturate today’s SATA spec,
pumping roughly 550MB/s of data through the
SATA 6Gb/s interface, whereas the fastest
7,200rpm hard drive would be lucky to hit
150MB/s across the platter. Other benefits of
SSDs are that they generate no noise since
there are no moving parts, which also lets
them produce much less heat. They can still
get a little warm, but don't require active
cooling like a hard drive does. And since they
have no moving parts, you're free to wedge
one into your laptop and toss it around like
the bouquet at a wedding, though we don't
recommend doing that. To summarize, SSDs
offer tremendous speed, emit no noise, give
off very little heat, and fit in the space the size
of a few credit cards. What's not to love?
What’s Not to Love
Here's the downside: SSDs are expensive, and
there's also the chance that whatever drive you
select might die on you one day. Now, we
know that doesn't sound good, but there are
some silver linings here. The first is that prices
are dropping rapidly, so much so that right
now 128GB drives are hovering around $100,
so that's less than the magical $1-per-gigabyte
price bar we’ve set for an OK deal. Drives with
capacities of 256GB are even less expensive,
averaging around $160. Sadly, 512GB drives
are still a smidge spendy, and 1TB drives, well,
they don't even really exist for mere mortals.
SSD prices will continue to fall, though, as
adoption rates increase, so any financial
barrier to entry you might fear will soon be
nonexistent.
The second point is much more concerning to
you, as nobody enjoys seeing their data go
bye-bye. Let's just get this out of the way:
Many people have had their SSDs fail. We've
had our own personal SSDs fail in our home
machines, and seen units here die an untimely
death in the Lab, in seemingly random fashion.
What needs to be made clear, though, is the
fact that in all of these cases it was the
controller that gave out, not the NAND flash
itself. Anyone who tells you they have reached
the end of the life cycle for NAND flash is
either high, lying, or from the Internet, so
don't believe them. It's not the flash that
typically dies, but the controllers, and here's
the good news: Things are improving massively
on this front. In fact, we've yet to see a late-
model SSD die, and chalk up the earlier
failures to the fact that it was simply new
technology, not yet battle-tested on the front
lines. You might recall several high-profile SSD
recalls, as well, which didn't help their status
as a fledgling technology. The simple truth is
that those days are mostly behind us, and as
controller and firmware technology has
matured, reliability has improved greatly, so
we have zero problems recommending any
late-model SSD but, as always, you should back
up your data regardless of the storage medium
you have in place.
The Evolution of SSD Form Factors
When SSDs
first burst
onto the
scene, they
came in
unwieldy
3.5-inch
enclosures
the size of hard drives. These SSDs were
blazing-fast at the time, and ungodly
expensive. We're talking $1,000 for 64GB, but
back then it was all that we had, so we paid it.
SSDs eventually migrated to the 2.5-inch
enclosures that we use now, and are also
offered in the teeny, tiny mSATA form factor
for notebooks, as well. If this downsizing trend
continues, we expect future SSDs to be
microscipic.
Anatomy of an SSD
1. Outer Shell
This shell could be plastic or metal, and helps
absorb some of the heat from the flash
memory inside. A 7mm shell allows an SSD to
be used in an Ultrabook, though some employ
the thicker 9mm form factor. Unlike with a
mechanical hard drive, you could remove this
cover and run an SSD commando and it would
not make much difference to the drive, though
we don't recommend it.
2. NAND Flash
These are the memory chips that hold your
data. They are typically clustered in groups of
chips covering both sides of the PCB. Most
SSDs you will see use either MLC or TLC NAND,
though if this was an enterprise-level model it
might use SLC NAND flash. MLC flash wears
down twice as fast as SLC flash, and TLC wears
down quicker than MLC, but you will still get
many years of usage from MLC or TLC.
3. DRAM Buffer
Every SSD also includes a bit of DRAM used for
buffering purposes. Like cache on a hard drive,
data is stored here temporarily before it's
written to the device. Wear-leveling data is
also placed into the cache while the drive is
running. SandForce SSDs are the only models
that do not use external DRAM.
4. Power and DATA Interface
Modern SSDs ship with SATA 6Gb/s interfaces
that allow for roughly 550MB/s read and write
speeds, though this will change soon since
today's drives are saturating the bus. The next-
gen interface, called SATA Express, will utilize
PCI Express lanes instead, allowing us to
eventually hit up to 16Gb/s of throughput. Yes,
we are salivating.
5. Controller
The controller runs the show, usually with a
multicore processor. This is what separates
one SSD from another, for the most part,
though custom firmware designed by the drive
manufacturer is also a factor. Controllers
communicate with NAND over parallel
channels, compress and uncompress data, and
keep the drive optimized with garbage
collection.
Solid-State Terminology
Or how to look like you know what you’re
talking about
NAND Flash
NAND flash is a type of nonvolatile flash
memory that stands for "Not And," which is a
reference to the type of logic gate it uses. This
is different from NOR flash, which is used in
environments where the same program is run
over and over again. NAND memory is popular
due to its speed, durability, and relatively low
cost compared to DRAM, and is commonly
found in storage devices such as USB keys,
tablets, cell phones, and of course, SSDs.
Though there are various types of NAND flash,
all SSDs on the market currently use this type
of memory.
Controller
This is the brains of the SSD and what truly
separates one drive from another, as they
mostly use very similar NAND flash. Typical
controllers today use multiple cores for
running the drive, performing data
compression, and executing drive
optimizations. Before you make any purchasing
decisions about an SSD, find out which
controller it uses, as some controllers have a
checkered history. Currently only Samsung and
OCZ have controllers that were designed and
manufactured in-house, which theoretically
gives them an advantage, while Intel uses
SandForce, Corsair uses Link A Media, and
Crucial uses a Marvell controller.
MLC NAND
This is the most common type of NAND flash
used in SSDs today, and it stands for “multi-
level cell” memory. Its much more expensive
counterpart is SLC, or “single-level cell”
memory. In SLC, only one state can be
maintained per cell, making it good for one bit
of data. In MLC, however, up to four states can
be stored per cell, allowing it to hold two bits
of data. The proximity of the two states creates
the possibility for more errors, though, which
is why SLC is so expensive, and rare. Flash
memory can only sustain a finite number of
read/write operations but modern day SSDs
perform wear-leveling in order to allow them
to survive for a decade or longer depending on
drive activity levels.
SLC NAND
This is the good stuff. SLC NAND is very
expensive and is only found in enterprise-level
storage products due to its cost. It stores one
data state per cell, and since there are no
other data states nearby, it is extremely
accurate and long-lasting. At press time a
256GB SLC SSD costs $2,600, so you won't be
seeing them in your home machine any time
soon.
Trim
Trim is something you'll hear about a lot with
SSDs, because it performs the crucial function
of helping the SSD optimize itself when it is
idle, so not having Trim support is bad, and it
needs to be in both the drive and your OS.
Essentially, the Trim command is sent from
the OS to the drive's controller to tell it which
bits of data can be safely deleted, so without
Trim the drive could theoretically just fill up
and degrade. Since NAND cells cannot be
overwritten, they must be erased before new
data is written to them. The command also lets
the controller reorganize data, similar to
defragmenting a hard drive. Trim is supported
in Windows 7 and 8, and in all modern SSDs.
Asynchronous vs. Synchronous Flash
You'll see this in an SSD's specs, and the
bottom line is that asynchronous flash is not
as fast or expensive as synchronous flash, so
it's not uncommon to see it in value drives,
while synchronous flash is used in high-
performance drives. Synchronous flash
processes data roughly twice as fast as
asynchronous, on both ends of the clock cycle,
so you get two outputs per cycle, while
asynchronous is not synced to the clock speed
of the processor, so you can expect lower
performance.
IOPS
This spec shows how many operations per
second the drive is capable of performing. This
differs from read/write speeds in that it's not
measuring the speed of the writes or reads,
but the number of them. This is typically used
in situations where heavy random workloads
are needed, simply because, in our opinion, it
sounds better to say 85,000 IOPS than 30MB/
s.
Sequential Read/Write Speed
This is how fast a drive can read and write
contiguous data, sort of like an elephant
inhaling a row of peanuts. This is often used as
a metric for benchmarks because it measures
"straight-line speeds" but is not indicative of
real-world performance, as data is rarely
written or read in this fashion.
Secure Erase
Old blocks of data on an SSD have to be erased
before new blocks can be written to it, which
takes time, so the fastest an SSD will ever be is
the moment it comes out of the box and is
totally empty. Unfortunately, even if you
deleted everything on the drive, the data is
still there, so it will still need to be erased if
you want to write over it (Trim does this to
some extent but not completely). The only way
to totally wipe a drive of all its contents is a
Secure Erase, which completely deletes all data
on a drive. This is the most common way to
get an SSD back to its fastest possible state,
and is accomplished via software included with
your drive.
The Downside of Using Trim
The Trim command has been made into
something of a living legend in Windows 7 and
8, because it is so crucial to keeping an SSD
optimized via garbage collection and the
deletion of data that is no longer needed. Since
SSDs require a data block to be erased before
it can be written to, it’s important to have that
deletion occur before the data needs to be
written, otherwise the whole process gets
bogged down with multiple operations instead
of just a simple write command.
There’s a big downside to keeping your drive
optimized, though, which HDD users don’t have
to contend with: If you accidentally delete a
file and then try to undelete it via recovery
software such as File Scavenger you may be
out of luck. That’s because Trim, or even the
drive’s own firmware, may have already
deleted the data forever. More disturbing is
that Trim can be executed at any time—its
schedule isn’t transparent to the user—so 10
minutes after you’ve deleted the file, it might
already have been purged.
If you are a serial file-bungler and find
yourself in constant need of file recovery,
consider disabling Trim to buy you a little
more time to recover inadvertently deleted
data (at the cost of overall performance).
Windows 7 users should also consider leaving
system protection on, which will, on occasion,
make copies of files. Windows 8 users should
enable the File History feature that makes real-
time backups of files on a secondary drive for
you.
The Software Side
SSD utilities can make all the difference to
your drive’s overall functionality
Though most people install an SSD and never
give it a second thought, free software makes
it possible to monitor, optimize, and tweak a
drive’s performance. Samsung, Intel, and OCZ
SSDs come bundled with free utilities, and you
can use the free CrystalDiskInfo (http://bit.ly/
UKzt0 ) with any SSD on the market. Here’s a
quick peek at what each one offers.
Samsung SSD Magician 4.0
It’s hard to believe, but not only does Samsung
make arguably the best SSDs available right
now, but it also makes the best SSD software,
as well. Right on the home screen you can see
how much data has been written to the NAND,
its status, your interface speed, and more. If
your OS doesn’t support Trim, you can click
“performance optimization” to Trim the drive
manually. You can also update the firmware,
adjust over-provisioning space, and more.
Samsung regularly updates its software, too,
making the choice to invest in a Samsung SSD
that much easier.
Intel SSD Toolbox
Intel’s toolbox software is easy to use, full of
information, and tells you right on the home
screen what the drive’s health status is at the
moment. Diving deeper into the menus will let
you update the drive’s firmware, perform a
secure erase, run diagnostic scans on the
drive, run the Trim command, and it will show
you how to fully optimize the drive with your
OS. If you’re super-nerdy you can also choose
to examine the drive’s SMART data and details,
but the whole point of the simple interface is
to show you all that data in an easy-to-digest
fashion. Still, it’s all there if you really want to
see it.
OCZ Toolbox v4.3
OCZ’s free Toolbox software is basically the
equivalent of a three-blade Swiss Army knife,
in that it only lets you do a few things with
your SSD. It’s actually strange that OCZ would
spend time and money to develop a software
tool, then populate it with so few options, but
since it’s free software we’re not complaining
too much. The tool gives you the ability to
check for firmware updates and apply them,
and perform a secure erase of the drive; it will
also spit out the drive’s SMART data in the
most unfriendly manner we’ve ever seen, so
have fun translating it. This utility is helpful
for updating your drive’s firmware but not
much else.
CrystalDiskInfo 5.4.2
This is a free utility that should be able to read
the SMART data from any SSD and give you an
indication as to the drive’s health, information
about its activity, and more. One field to pay
attention to is Total NAND Writes, as that will
give you an indication of how much has been
written to the drive if you like to keep tabs on
those things. It also displays the current
firmware version, SATA transfer mode, which
features are enabled, and all the SMART data,
as well.
