Everything You Wanted to Know About SSDs

Josh Norem

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 junkie 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.

Click the next page to learn about solid-state drive terminology and the software side of SSDs.

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.

See the next page to read about the downside of using Trim and to learn about different SSD software.

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.

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