HDD versus SSD: Which is Best?

08 Jul 2010

by: Staff

Trying to decide between using solid state drives (SSDs) and hard disk drives remains an apples and oranges affair. Sure, there advantages to going solid state, but there are some clear disadvantages too, and they aren’t like to clear up anytime soon, so don’t trash your hard drives yet.

GROUND zero in this debate is cost. Storage costs a lot – upwards of 40 per cent of the total cost of system ownership when it comes to video surveillance solutions. And current numbers indicate that SSD costs three times as much as HDD. The upshot of this is that it would be quite possible to install an SSD system that cost as much your HDD-supported entire solution. Yikes.

Of course, SSDs have good points. Because they don’t have the actuator arm to read the platter that’s at the heart of an HDD, they read and write to disk faster. This is a big advantage – especially if you were installing big megapixel cameras and money was no object.

If your surveillance application demands a lot of read and storage and you only have a small storage volume demand there’s no doubt whatever that going SSD will give you a very noticeable performance boost – especially if you are storing at HD resolution (720p) or higher.

According to IT industry commentators, consumer-grade SSDs cost around $3 per gigabyte, while traditional hard drives cost about 20 to 30 cents per 2.5-inch gigabyte or 10-20 cents for 3.5-inch desktop and server drives. That’s a really big difference.  

But prices for SSD are falling you say. Well they are but according to IT research outfit Coughlin Associates’ founder Tom Coughlin, per-gigabyte prices for HDDs and SSDs are dropping at the same pace - about 50 per cent each year and that means the comparative expense will remain. Meanwhile, 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."

A recent ComputerWorld review undertaken by Lucas Mearian pitted a couple of 2.5-inch laptop drives - a Seagate Momentus 7200.4 500GB HDD against an OCZ Vertex Series SATA II SSD.

Mearian tested parameters like the impact of each drive on battery life, the read and write speeds, cold boot-ups and restarts, and CPU utilization – all meat and potatoes stuff for video surveillance people.

“As you'd expect, the two drives I tested have vastly different prices,” says Mearian. “The Seagate Momentus HDD (model - ST9500420AS) will run between $127 (all prices in US dollars, people) 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.”

Meanwhile, 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.

According to Mearian, most SSD vendors publish sequential read/write rates, which are much faster than random I/O but he explains 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.

How this applies in a video surveillance application depends on your set-up. If you’re using record on motion, then read/write is less of an issue – but constant recording is another matter.

“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,” explained Mearian.

“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.”

Test times