Over the years, the good old magnetic platter has undergone many changes that have made hard drives a commodity and drastically driven down the cost of storage. Today, storage costs anywhere from about 30 cents per GB for SATA drives to $3 per GB for enterprise-grade SAS drives. Of course, this is a rough estimate that varies wildly based on drive capacity, manufacturer, RPMs, etc. For the purposes of this post, it's a close enough estimate.
Recently, however, a relatively new contender - the solid state drive (SSD) - has emerged in the storage game that could, over time, seriously shake up the storage market. Although solid state storage has been around for a while in the form of USB-powered flash drives, the technology is evolving to a point where SSDs can, in some cases, start to supplant traditional storage. However, solid state storage is very different from traditional storage in a number of ways.
Unlike their mechanical counterparts, solid state drives have no moving parts. Instead, a solid state storage device uses either volatile or non-volatile memory to achieve its storage capabilities. Units that use DRAM-based technology (volatile memory) basically have a bank of RAM installed that takes the place of a hard drive. Since data stored in DRAM cannot survive a power loss, these kinds of devices often have backup storage that can be used in the event of a power failure. Although extremely fast, this kind of storage is not adequate for general storage in the enterprise.
SSDs become acceptable in some situations in the enterprise when the disks are built using non-volatile flash memory. Although slower than DRAM-based SSDs, flash-based SSDs do not require battery backup and provide much more reliability -- mainly since the stored data can survive a power failure.
Until recently, SSDs were not cost-effective replacements for traditional hard drives. With a current approximate price tag of $10 - $20 per GB for SSD-based storage, it isn't going to immediately supplant magnetic hard drives for most organizations. And, in the data center, SSDs are probably a very long way off. Once the price of SSD-based storage comes down to the high end of SAS, you will likely see more manufacturers creating enterprise-grade storage arrays based on flash.
In the meantime, however, there has been significant interest in SSDs for mobile devices. Even though SSD-based storage is more expensive, with lower power consumption, lower levels of heat, and similar (if not better) performance, putting SSDs into a laptop or other mobile device makes a lot of sense.
Solid state drive disadvantages
Besides the price, SSDs do have some disadvantages when compared with traditional magnetic media, although some of these downsides have been mitigated.
First, flash-based storage device blocks (each flash device is broken into blocks) have a limited number of write cycles before they wear out. Older flash controllers did not do a good job managing the location of written files, so some blocks of the flash device might be used over and over while other blocks remain completely untouched for the life of the device, thus limiting the device's potential lifespan. Newer controllers do a much better job of managing write locations so as to maximize the life of the disk. In fact, with the optimal write method and usage pattern, a flash device can even outlive a magnetic disk.
Second, SSD capacity remains much lower than that provided by magnetic media and will for some time. Although there are 160GB SSDs out there, compare that to the recent announcement of 1TB magnetic hard drives. When it comes to raw storage, magnetic media can't be touched yet.
Another major downside to flash-based devices is the difficulty of data recovery. Often, when a flash drive fails, it's done. End of story. With magnetic disks, there are tried and true methods to try to recover information. (Have you ever put a hard drive into a freezer? It works.) Although information can sometimes be recovered from a flash device, it's much harder and much less of a certainty.
Finally, although solid state drives shine when used with random I/O, they do not do as well as magnetic media when it comes to sequential I/O.
For the enterprise, SSDs will be limited to portable devices and low capacity requirements until two things happen: (1) The price per GB drops significantly, and (2) the device capacity increases significantly. Once those two things happen, the fight will be on.