Review: Hard disk vs. solid-state drive -- is an SSD worth the money?

SSDs have the speed, but HDDs have the capacity

Solid-state disk (SSD) drives are all the rage among techies. The drives use non-volatile NAND flash memory, meaning there are no moving parts. Because there is no actuator arm and read/write head that must seek out data on a platter like on a hard disk drive (HDD), they are faster in reading and, in most cases, writing data.

But SSDs are also much more expensive than their hard-disk drive (HDD) counterparts, which offer 300GB of capacity or more for less than $100.

Most consumer-grade SSDs from leading vendors now cost around $3 per gigabyte, while traditional hard drives cost about 20 to 30 cents per gigabyte for 2.5-in. laptop drives and 10 to 20 cents per gigabyte for 3.5-in. desktop drives, according storage market research firm Coughlin Associates Inc. In other words, even the cheapest 120GB SSDs are going to be around $300, though some are available on sale for less. So should you buy a high-capacity HDD for little cash or plunk down hundreds of dollars more for a fast, but lower-capacity, SSD? Or, should you wait?

Coughlin Associates founder Tom Coughlin said per-gigabyte prices for HDDs and SSDs are dropping at the same pace -- about 50% per year -- so the sizeble price gap between the two will remain for years to come.

Gregory Wong, a solid-state drive analyst with market research firm Forward Insights agreed.

"I think the issue with SSD adoption is that prices have not been favorable," he said. "And there's still going to be a gap between HDD and SSD prices, even five years from now."

The average consumer in the market for a desktop or laptop doesn't pay a lot of attention to drive I/O speeds -- he tends to focus more on capacity. So when a drive offers less capacity, even when it's an SSD, it's apt to get passed over, according to Wong.

A lot depends on how you expect to use your computer. If you're a college student writing papers and surfing the Internet for information, the advantages of an SSD are negligible, but if you're downloading video and using multiple applications at the same time, an SSD will give you a very noticeable performance boost, Wong said.

Head to head: SSD vs. HDD

I decided to test two popular 2.5-in. laptop drives -- a Seagate Momentus 7200.4 500GB HDD and an OCZ Vertex Series SATA II SSD -- to determine the advantages each offers. I tested their impact on battery life, the read and write speeds, cold boot-ups and restarts, and CPU utilization.

I briefly considered pitting the SSD against a higher-end, 10,000-rpm Western Digital VelociRaptor as the test unit for the hard disk drive or using the 2.5-in Intel X25-E for the solid-state drive unit. The VelociRaptor yielded a 105MB/sec random read rate in Computerworld's testing and the X25-E blew by everything with a 250MB/sec peak read rate. But I wanted to evaluate something more accessible price-wise for the average consumer, someone who generally wouldn't normally wouldn't consider a top-end drive for her laptop or desktop.

Besides, even the VelociRaptor is no match for a decent SSD.

As you'd expect, the two drives I tested have vastly different prices. The Seagate Momentus HDD (model - ST9500420AS) will run you between $127 and $140, while the OCZ 120GB Vertex SSD goes for between $376 and $400. Both drives use a SATA 3GB/sec interface and both use cache to increase write performance. The OCZ has 64MB of cache, the Seagate, 16MB of cache.

SSDs are naturally more rugged than HDDs because they have no moving parts. OCZ claims its Vertex drive can sustain up to 1,500 Gs of shock before sustaining damage or a drop in performance. Seagate claims its Momentus drive can withstand up to 350 Gs while operating and 800 Gs when turned off.

The Vertex is OCZ's second iteration of an SSD, and it uses 64MB of cache to artificially enhance the write performance and a more advanced Indillinx controller than its slower predecessor, the OCZ Apex Series SSD, which uses a controller from JMicron and has no cache memory. The Vertex drive's packaging lists a maximum read rate of 250MB/sec and a sustained write rate of 100MB/sec. It also claims a 1.5 million-hour mean time between failure (MTBF) rate, if MTBF can actually be applied accurately to an SSD. Most experts don't believe it can.

(Keep in mind that most SSD vendors publish sequential read/write rates, which are much faster than random I/O. But most operations on a desktop or laptop are random. For example, file systems and e-mail applications mostly use random operations, while system boot up or copying a large file from a USB drive involves sequential operations. So, in general, don't believe the packaging hype.)

The Seagate Momentus 7200.4 marketing material offers no read/write rates, nor does Seagate offer any information other than a seek time on its Web site: 11 milliseconds for reads and 13 milliseconds for writes. Seagate doesn't use MTBF, preferring its own annualized failure rate (AFR) metric as a method to gauge drive reliability, which is .5%.

The SSD easily beats the HDD in weight. Seagate's Momentus weighs 3.85 ounces; OCZ's drive weighs 2.7 ounces.

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More about: ATTO, eGrabber, Intel, Micron, OCZ, Seagate, Vertex, Western Digital
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