Hard Drives vs. Flash SSDs
We’ve been looking at the flash SSD market for quite a while, which has solutions that deliver up to 130 MB/s of read throughput. The next generation, as announced by companies such as OCZ and Intel, is going to offer up to 200 MB/s of read throughput and higher capacities. Still, it remains questionable as to whether or not these new products will be able to provide balanced performance. This means that write performance, access time, and I/O performance must be at levels comparable to the impressive read throughput, and they should also deliver on the promise of reduced power consumption at the increased capacities.
Flash SSDs do not have any cache memory, since the flash cells are typically fast enough to turn simple DRAM cache into a useless feature—the transistor-based technology ensures that access times are almost nonexistent. While conventional hard drives take between 5 and 25 milliseconds to locate and access stored blocks, all content on a flash SSD can be accessed directly and nearly instantly. As a consequence, flash SSDs are not only fast to find data, they do not require defragmentation. (In fact, defragmentation increases the wear of the flash memory cells, which only allow for several thousand read/write cycles.) While long-time studies still aren’t available, the life span of a flash SSD should at least be in the same range as the component design life for mechanical hard drives, which typically is five years.
MLC vs. SLC
Flash SSDs have the potential to easily outperform any conventional hard drive by delivering much higher read throughput. Write throughput and access time depend on the flash technology that is used: multi-level cell flash (MLC), stores several bits per cell, making it cost-effective, but slower. In contrast, single-level cell flash (SLC), is faster but more expensive.
Flash Loses the Cost Comparison
For the time being, conventional hard drives will still win every comparison with flash SSDs once cost and capacity are added to the equation. Most SSDs are still limited to 32 and 64 GB capacities, and if you go for fast SLC flash drives, the price tag will have more than three digits. MLC-based flash reaches 128 GB today, which can be considered an acceptable capacity, but not all of these drives can be recommended, as they usually have some disadvantages like low power efficiency or slow write performance.
On the other hand, conventional hard drives offer up to 500 GB of capacity today, and are holding up rather well when it comes to throughput, as you will see in the benchmark section of this article. Access times are an issue, though: HDDs can’t compete here. However, many HDD products are much more efficient than previous generations, and price is the killer argument. A 320 GB conventional drive costs less than $100, and if you go for high performance at low cost, you can get 80 to 120 GB at 7,200 RPM for less than $70.
Editor’s Note: The following storage stories shed additional light onto the mechanical vs. SSD issue.
Flash SSD Update: More Results, More AnswersWe found that many Flash SSDs do not deliver on their promise of being power efficient. The latest generation, however, manages to combine performance end efficiency impressively. Even so, Flash SSDs don’t offer sufficient capacity to actually store more than your operating system plus applications and the basic files you might need.
Will SSDs Take Over The Enterprise?Eight Memoright state-of-the-art Flash SSDs battle Seagate’s Cheetah 15K.5 and Savvio 10K.2 in RAID configurations. Flash SSDs turn out to be far superior when it comes to I/O-intensive workloads, while they don’t necessarily beat mechanical hard drives when it comes to throughput.