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Hard disk drives vs. solid-state drives: Are SSDs finally worth the money?

Editor’s note: This story is excerpted from Computerworld. For more Mac coverage, visit Computerworld’s Macintosh Knowledge Center.

Three years ago, I wrote a story comparing hard disk drives to solid state drives (SSDs) based on capacity, performance and cost. A lot has changed in three years. For one, laptops are quickly being eclipsed by tablets, which have NAND flash memory embedded on their motherboards. In addition, operating systems have been optimized to take advantage of SSD I/O performance. SSDs today are far more reliable, have greater endurance and perform better (in some cases, two to three times better) than in 2009.

There are also new SSD categories. For example, hybrid drives combine NAND flash cache memory with a spinning disk in a hard-drive form factor. In addition, in adherence to Intel's new ultrabook computer specifications, manufacturers are beginning to produce laptops with two drive slots, one for a hard drive and the other for a low-capacity cache SSD which works with hard disk drives to speed up boot and application load times.

Perhaps the single biggest change, though, is price. In 2009, SSDs cost around $3 per gigabyte. That meant a 120GB SSD cost more than $300. If you were paying $700 for a laptop, it wasn't reasonable to expect to pay almost half that for a new drive.

Today, however, SSDs cost close to one-third of what they did in 2009—in many cases, less than $1 per gigabyte. For example, Crucial in July announced its new low-cost v4 SSD that costs $100 for a 128GB model and $190 for a 256GB model. This isn't unexpected; in January 2012, research firm IDC predicted that prices of SSDs would tumble this year. (Of course, hard drive prices have also plummeted. These days, you can pick up a 7200-rpm, 1TB laptop hard drive for a little more than $100.)

One thing hasn't changed, though: While they may never beat out hard drives in price, SSDs will always have one major advantage: No moving parts. This means no mechanics to break, even when a machine is jostled or dropped. SSDs are natively more resilient than hard drives, particularly when it comes to mobile applications.

Comparing SSDs and hard drives

I tested an SSD and a popular, well-performing consumer hard drive to see how they rate for performance, cost, and general usability: the Intel Solid-State Drive 520 Series (240GB capacity; $275 to $415) and Western Digital's 500GB WD Black (previously called the Scorpio Black), a 7200-rpm 2.5-inch hard disk drive with 16MB of DRAM ($112 to $262). I also checked out a hybrid drive: Seagate's Momentus XT Solid State Hybrid Drive (750GB; $195 to $324), which includes a 7200-rpm 2.5-inch drive with a SATA 6Gbps interface. A 500GB version of Momentus sells for as little as $90.

(When requesting test units, I asked the companies for their highest-capacity review models. While capacity affects SSD performance, it really doesn't affect hard drive performance—at least, not until the drive is filled.)

For the benchmark tests, I used an Apple MacBook Pro running OS X Mountain Lion, with 8GB of RAM and a 2.3GHz Intel Core i7 processor.

To measure read/write performance, I used the Blackmagic Disk Speed Test. To determine file transfer speeds, I used a 1.19GB folder that held 327 jpeg images. The file was transferred from a desktop folder to the hard drive. Additionally, I tested application load time by opening a 10MB PowerPoint presentation and a 372-page, 300KB Microsoft Word document.

The Intel 520 Series SSD

According to the specifications from the manufacturer, the Intel 520 Series SSD had the best performance potential of all three drives I tested. The SSD was actually tested on two separate platforms: First, I ran the tests described above using my MacBook Pro with an SATA 3.0 internal drive interface. However, because SSDs will perform better right out of the box than after they've been filled with data, I decided to also send the SSD to a professional drive testing service, Calypso Systems, which benchmarks drives for drive vendors and system manufacturers.

Intel 520 Series SSD

Microsoft Word opened in about 2 seconds, which would allow a user to begin writing to the top of a document, or reading it, regardless of its size. However, the Word document took 57 seconds to load all 372 pages, so you couldn't access the later pages until it had finished loading. Opening a 10MB Power Point presentation took 2 seconds. Copying the 327 jpeg images took 15 seconds. The Blackmagic benchmarking software recorded a maximum read rate of 456 MBps and a write rate of 241 MBps using 4KB blocks.

Intel's specification sheet states that the 520 Series SSD sports sequential read/write speeds of 550 MBps. and 520 MBps, respectively. I'm guessing that those specs were attained using higher-end hardware, such as a storage array.

I also tested the Intel 520 SSD on a MacBook with a SATA 2.0 3 Gbps interface. The read/write speeds dropped significantly—in this case, the 520 Series SSD offered a maximum sequential read and write rate of 280 MBps.

Intel's drive also took it easy on laptop batteries, sipping a maximum of 5.25 volts while operating and only 600 milliwatts when idle.

Calypso Industries uses the Solid State Storage Initiative Performance Test Specification (SSS PTS) and a standardized hardware platform to evaluate and compare drive performance. Developed by the Storage Networking Industry Association, there is no more accurate method to test drives.

The SSS PTS method requires that drives first be "conditioned" prior to testing, meaning data is written to the SSD until its performance levels out. New SSDs perform better than used ones because their controller chips don't have to move existing data around to accommodate new data writes. They can just stick the data anywhere without "thinking" about it.

Once all the blocks of an SSD have been used, however, then operations get more complicated and drive performance slows and then levels out. So the SSS PTS methodology calls for filling a consumer-class SSD to 75 percent of its capacity twice before it is tested so that the results reflect real-world performance.

Calypso's throughput tests showed the Intel SSD handily outperforming both the hybrid drive and, not surprisingly, the hard drive. The SSD had a blazingly fast top random read throughput of 505 MBps, and a random write rate of about 225 MBps. More importantly, the Intel SSD had an average "steady state" throughput of 223 MBps. This means that most read and write operations will be performed at 223 MBps.

Western Digital WD Black hard drive

Unlike the two other drives I tested, the WD Black uses a SATA 2.0 (3 Gbps) interface, not a SATA 3.0 (6 Gbps) connection. Manufacturers don't make laptop hard drives with a SATA 3.0 interface because the drive's performance can't even fully use a SATA 2.0 interface.

Western Digital Black hard drive

After I installed it into my MacBook Pro, the drive booted up in 20 seconds. Restart took just 21 seconds. While that's not SSD or hybrid drive load time, it's not that far behind; the speed can be attributed to the generous amount of DRAM on board. As the drive fills up over time, I would expect those bootups to slow down significantly.

Opening a 300KB, 372-page Word document took 10 seconds, then an additional 38 seconds to load all the pages. The second time I opened the document, the RAM cache obviously kicked in. The Word document opened in 2 seconds, and all 372 pages took only 25 seconds to load. The third time I opened it, Word again loaded in 2 seconds and the entire document loaded in 7 seconds, beating the SSD and hybrid drive alike. I had not expected that. Opening a 10MB PowerPoint slide took just 2 seconds, the same time as the hybrid drive and the SSD.

Using the Blackmagic Disk Speed Test, the WD Black showed a sequential read/write performance of 122.2 MBps. and 119.6 MBps, respectively. Random performance is where the drive fell flat: the disk had a random write performance of 67.6 MBps and a random read performance of 34 Mps. Random performance is particularly important as the drive begins to fill with data and the read/write head must move across the spinning disk to locate the information you want. That requires more and more time as more data fills the drive.

Seagate Momentus XT Solid State Hybrid Drive

Hybrid drives can be a bridge between hard drives and SSDs. They offer SSD performance on critical operations such as boot up and application load times, and provide vastly higher capacities for the money than an SSD.

Fang Zhang, an analyst with IHS iSuppli, says most consumers purchasing a $700 PC or laptop aren't going to spend hundreds of dollars on an SSD. Hybrid drives, on the other hand, can be had for as little as 14 cents a gigabyte. For example, a 500GB Seagate Momentus XT can be purchased on Amazon for $70. The owner of that $700 laptop would be a lot more willing to spend one-tenth the price for a significant storage-performance upgrade, Zhang contends.

On the other hand, is that what consumers are most concerned with? I don't think so. I believe that the average consumer is more concerned with capacity than performance. And with a hybrid drive, you get both.

But while hybrids offer significant performance improvements over traditional hard drives, like hard drives, they have mechanics (moving parts). If you drop your laptop while it's powered up, there's a chance you'll damage the hard drive component of a hybrid drive. That's another factor to think about when deciding what type of drive to get.

Seagate Momentus XT Solid State Hybrid Drive

During its initial OS installation, the Momentus XT captures boot files and places them in a special segment of the NAND flash where they remain for the life of the drive. The feature ensures that the drive always boots from flash and not from the spinning disk.

The drive also has an Adaptive Memory algorithm that monitors which applications and data are initially loaded into a system and then "learns" to place that data on the SSD to speed up performance. Over the course of three boot-ups, system performance becomes optimized to each user's preferences.

In my benchmark tests of the Momentus XT, the initial boot up took 20 seconds, the same as the WD Black hard drive. Then I rebooted and the Adaptive Memory firmware kicked in and began optimizing the drive for my system. The second boot took 15 seconds; by the third boot, the drive was down to 12 seconds. Very impressive.

Copying the 327 jpeg images took 29 seconds. Opening a 300KB, 372-page Word document took 1 second and then an additional 57 seconds to download all 372 pages. On the second try, opening the Word document took 1 second again, but all 372 pages loaded in only 15 seconds. By the third try, the cache had really kicked in and it loaded all 372 pages in 10 seconds.

When it came to using the Blackmagic benchmarking software, there was an obvious problem: The software shows only the Momentus XT's hard drive performance, and that doesn't really reflect the drive's true capabilities. With that in mind: For sequential read/writes, the Momentus XT showed 106 MBps and 114 MBps, respectively. On random read/writes, the drive came back with 99 MBps and 90 MBps, respectively. Those results demonstrate that the SSD was not in use for these functions; these read/write speeds came from the spinning disk in the drive. And, while very respectable for a hard drive, the results come nowhere near SSDs' results, which are anywhere from 200 GBps to 250 GBps.

If you're looking for a hybrid drive, there aren't a lot of choices out there. There's Seagate and, well, Seagate. Last year, SSD maker OCZ introduced its RevoDrive hybrid drive, but it came in a PCIe card form factor—unusable in a laptop. The RevoDrive is targeted for workstations and for people working with high-bandwidth applications like video production, as well as gamers who love the performance that a high-end, high-priced desktop system offers.

Both Toshiba and Western Digital are rumored to be developing hybrid drives, but neither company would confirm that anything is in the works.

Even if they never catch on in a big way, I think hybrid drives have a lot to offer the average laptop user and they should be considered by anyone who is upgrading a laptop or desktop system.

Bottom line

I recommended an SSD in 2009. Now, in 2012, I do it with even more enthusiasm. To begin with, prices have dropped significantly. If you can afford to spend a couple hundred dollars on even a 128GB SSD, it's a superior proposition to even a 1TB hard drive. Why? The overwhelming majority of end users will never fill a 1TB internal drive, while just about everyone will be able to appreciate the incredible performance boost that an SSD provides. For the money, there is no other system upgrade that will give you the performance boost of an SSD. That goes for consumers and data centers alike.

One caveat, though: Some may say that SSDs do not stop working or slow down over time, as hard drives do. I've been using SSDs in my personal computers for years now. Some do die and, just like a hard drive, they do slow down over time. Don't let anyone tell you different.

If you do decide to go with an SSD, it's best to order it when you first buy your system. That way, it can be configured correctly by the manufacturer, which will optimize performance and ensure your system's warranty isn't voided.

However, even if you decide to throw an SSD into your existing system as an upgrade, you'll still experience a significant boost in performance, particularly on boot-up and application load times.

If you don't have a few hundred dollars to plop down on an SSD, a hybrid drive is an excellent alternative. Of course, you're still dealing with a mechanical drive that can break if a laptop is dropped while the drive is running, but you'll still get performance vastly superior to a hard drive.

In the very near future, however, buying your own SSD may become a moot point as new ultrabooks and other lightweight systems enter the market. At that point, you may want to consider an entire system upgrade.

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