The market is suddenly awash in solid-state drives thanks to the growing abundance and greater reliability of flash memory. Here’s what you need to know about today’s SSD storage.
Solid-state drives are new to the PC storage front, and they’re making waves by offering blistering speeds and greater reliability than traditional hard disk drives. For that, you can thank the NAND flash memory chips that make up every solid-state device.
If you’re not familiar with NAND memory, you need only look at your keychain. NAND is the technology that powers the storage on your USB thumb drive… and your mobile devices and the memory card in your digital camera. Whereas your tiny flash card might use but a single NAND chip, SSDs use multiple chips to achieve their higher capacities.
Storage that uses flash memory is quite unlike the hard disk drives used to hold your computer’s data. The latter rely on speedy actuators to read and write information on spinning magnetic platters. SSDs use electrical charges to read and write the state of individual flash memory cells. An SSD’s flash memory is nonvolatile: Unlike your computer’s RAM, an SSD drive retains your data when you switch the power off. And since the handshake is electric, SSDs can access that data in a fraction of the time it takes a mechanical hard drive to do so.
Sounds ideal, right? Actually, the performance potential of SSDs needs to be weighed against some significant drawbacks. We’re going to outline the pros and cons of the technology and how it compares to traditional hard disk storage. We’re also going to put seven leading solid state drives to the test and let the benchmark numbers do the talking. At this stage in the storage race, an SSD is a big investment; we want to help you maximize your return.
Before you make the move from a hard disk drive to a solid-state solution you need to be aware of what you’ll gain and what you’ll give up
An SSD’s biggest boon is its performance potential. Unlike hard drives, SSDs don’t have to wait for a physical arm to move read and write heads to specific points on a spinning magnetic platter. Reading from flash memory is a virtually instantaneous process, giving SSDs the ability to reach faster random read times and greater read throughput than magnetic hard drives.
Another advantage to SSDs is their relatively long life span. The NAND flash memory cells found in SSDs can last for years beyond the three- to five-year life expectancy of a magnetic hard drive. Because hard drives include numerous moving parts, they are vulnerable to wear and tear over time, especially if dropped or jostled.
An SSD can still break if you drop it, but as a whole, the lack of moving parts makes the category less prone to damage. If left unbothered, a solid-state drive can last up to 60 years longer than a hard drive in a similar desktop environment. And as an added bonus, SSDs don’t produce any noise and generate very little heat.
NAND flash is still a relatively expensive technology, limiting the capacities of solid-state drives and making for a high cost per gigabyte. Some manufacturers have managed to lower the cost of SSDs by using multi-level cell (MLC) technology to cram more bits of data onto a single memory cell. The problem is, MLC tech incurs a performance hit over single-layer cell (SLC) technology. The voltage complexities involved in maintaining the multi-bit cells can significantly slow the speed of write operations.
Unless a manufacturer specifies what kind of flash memory powers its drives, you won’t know whether you’re getting high-performance SLC or low-performance MLC flash. The price tag is the only distinguishing factor outside of benchmarks: MLC drives are among the cheapest SSD drives available (typically half the price of SLC SSDs).
Manufacturers claim SSDs offer better power savings than magnetic storage, but that’s not always true. This greatly depends on the construction of the drive: PATA- or SATA-based SSD drives tend to draw more power than typical hard drives.
Finally, SSDs can suffer from inferior random write and sequential write times because the data on an SSD is stored in kilobyte-size blocks. Adding more data to a block is a time-consuming process: The SSD copies the entire contents of the block to RAM, changes the data in the block, erases the original block of data on the SSD, and writes the changed block back to the SSD.
We’re using our standard storage benchmarking suite to compare seven solid state drives against two leading hard drives: Western Digital’s Velociraptor and Samsung’s HD103UJ—the fastest hard drive overall we’ve tested and the fastest terabyte drive we’ve tested, respectively. This will let us measure SSD performance against the two extremes of performance and capacity.
Our h2benchw benchmark is a synthetic test that measures a drive’s performance over a large swath of read/write operations. PCMark Vantage is our real-world benchmark, as it uses identical application traces to simulate common drive operations caused by normal desktop use. New to our benchmark testing is Adobe Premiere Pro. We use the app to generate an uncompressed AVI file straight onto a drive; the transfer rate of such a large file can tell a lot about a drive’s real-world ability to stand up to more demanding tasks.
Next: The Future of SSDs; Judging by the Numbers
Expect to see upgrades in controllers and NAND flash push SSD prices lower over time, but don’t hold your breath for either hard drives or SSDs to ever oust the other from the marketplace. According to Michael Yang, flash product marketing manager for Samsung, NAND flash capacities will continue to grow at a rate of 40 to 50 percent each year. This puts SSD development on par with the 40 percent capacity growth touted by top hard drive manufacturers.
A number of SSD manufacturers currently use PATA-to-SATA bridges in their SSDs, but it’s expected that these manufacturers will fully adopt the SATA 3Gb/s standard common to hard drives within 12 months. You can also expect to see performance upgrades to the actual NAND flash memory inside SSDs: In addition to block-size upgrades and an increase in SSD controller channels, read-ahead and caching algorithms will improve the drives’ write performance over the next five years.
Single-layer cell (SLC) and multi-layer cell (MLC) technology will continue to make up the flash cell foundations of solid-state drives. But according to Yang, SSDs will start moving away from the conventional form factors—1.8-inch, 2.5-inch, and 3.5-inch drive sizes—established by the magnetic hard drive market. This could bring forth SSDs of all shapes and sizes, an appealing prospect for notebook vendors that want more internal customization options.
You might not realize what you’re getting when you purchase an SSD. As we’ve learned from this roundup, the nuances of an SSD’s construction can make a huge difference in its performance.
We found that MLC-based drives just aren’t worth their low prices. While their read speeds are certainly impressive compared to those of the fastest hard drives we’ve tested, poor write performance holds them back. We wouldn’t use an MLC-based device as the primary volume for our operating system, especially since we can get hard drives that offer faster reads and writes at four times the capacity for the same price.
SLC-based drives are a different breed entirely. While their prices can vary from reasonable to outrageous, SLC-based SSDs can deliver a massive performance improvement in general operations thanks to their lower random access read and write rates. We would definitely recommend a less-expensive SSD, such as those from Samsung or OCZ, for a notebook environment. The combination of price and performance is great, and the added reliability—SSDs are less likely to fail than hard disk drives if you drop your laptop—sweetens the deal.
You don’t need this kind of protection in a desktop environment. It’s for this reason, and the capacity-to-cost ratio of even the least expensive SLC SSDs, that we cannot recommend this technology for desktops at this time. Or even for a while—we’d tolerate a 128GB SSD in our rig and would be happy with a 256GB product, but it will take a number of successive capacity improvements before such drives reach an acceptable price point.
All of the SLC SSDs we tested blew past a Velociraptor drive in simulated operating system patterns, as evidenced by the PCMark Vantage scores. But this speedy performance is of little value if Windows plus a game or two completely fills the drive. We’d rather stick with two $300 Velociraptors in RAID 0 right now: Based on our experience, an array of these drives is only 10 percent slower than the real-world performance of Samsung’s $800 SSD but offers nine times the capacity.
There will come a day when solid-state drive technology is a more compelling desktop option. Maybe NAND flash will get cheaper to produce or larger capacity SSDs will start bumping down prices on the lower-capacity end of the SSD spectrum. We can promise you one thing: Don’t expect this turnaround to occur for years. This is only the beginning of the storage war.
|RiData||Super Talent||Memoright||Samsung||OCZ||Imation||Mtron||WD Velociraptor||Samsung HD 103UJ|
|Average Sustained Read Rate||91.52||91.57
|Average Sustained Write Rate||22.69||22.90
|Random Access Read (ms)||0.39||0.39
|Random Access Write (ms)||248.04||246.10
|Premiere Pro (sec)||634||632
|PCMark Vantage Overall Score||9,541||9,577
Update: Since we published our SSD roundup in our November issue, we've also reviewed Intel's X-25M drive. Here's what Gordon Mah Ung, who reviewed that drive for us, had to say about this addition:
You can look at Inte’s 80GB X-25M two ways. From the perspective of laptop users, you finally get desktop performance (and beyond) in your portable. For desktop users, you can get RAID 0 performance without having to run the data risky configuration.
How good a performance? Against the six other SSDs, the Intel’s read speeds were roughly twice that of the closest competitor – the $1,500 Memoright. Even better, the Intel drive is selling for about $600. To give you an idea of how fast the Intel SSD is, a wickedly fast Western Digital 300GB Velociraptor tops out at about 98MB/s in reads. We saw a benchgasmic 206MB/s from the X-25M.
The Achilles’ heel of the X-25M is its write speed. At 64MB/s, it’s very respectable but not great. Oother SSD’s on the same MLC memory type as the Intel drive wrote in the 22MB/s range. The Memoright’s SLC memory let it write at 106MB/s while the Velociraptor burns bits at 98MB/s. However, we’d take the trade off as most users read data more than they write. Intel has an answer for the write speeds with an SLC-based drive that will write in the 200MB/s+ range. Drives using SLC, however, will have less capacity (initially 32GB) and cost a ton more cash.