Solid State Drives (SSDs) are rapidly gaining acceptance for enterprise data storage. But some companies remain reluctant to fully embrace the technology because of lingering concerns about the suitability of flash-memory for storage of mission-critical data. In many cases, however, issues that may have had some legitimacy several years ago are no longer valid. They have, in effect, become myths about SSD data that are contradicted by the facts.
In this article, we’ll take a look at several of those myths.
1. SSDs Are A Lot More Expensive Than HDDs
Since solid state devices were first introduced, they have cost more than equivalent hard disk drives (HDDs). But as flash memory technology has matured, prices have fallen steeply. Today the per-gigibyte prices of enterprise SSDs have already attained rough parity with those for the highest-performing HDDs. For example, Zadara™ Storage, in partnership with Intel, is offering SSD-based cloud storage at a price point equivalent to that of existing HDD products.
Moreover, because of factors like greater storage density, less power consumption, and greater reliability, overall costs associated with SSD storage are often lower than those for hard disks.
2. SSDs Have Less Storage Capacity Than HDDs
Until recently it was true that modern HDDs far outpaced SSDs in the amount of storage that could be packed into a given drive form factor. But that’s changing fast. Currently, the top of the storage density range for HDDs is represented by helium-filled drives with a capacity of 10TB. The prevailing industry expectation is that, due to constraints imposed by the laws of physics, spinning platter drives will max out their capacity potential at no more than about 40TB.
In contrast, 16TB SSDs are now on the market, and several manufacturers have announced 100TB behemoths they expect to make commercially available within the next several years. Clearly, the capacity advantage of HDDs over SSDs is already a thing of the past.
3. SSDs Have Shorter Life Spans Than HDDs
It’s true that SSDs wear out with use. (But, of course, so do HDDs). Each time a NAND flash memory cell is written or erased, it degrades by a tiny amount. Over time, the effects of these write/erase (or program/erase) cycles accumulate to a level where the device can no longer retain new data. To make matters worse, there is no way to consistently predict when a SSD will reach that point.
SSD providers use several methods to combat the write cycle limitations of their products. For example, wear-leveling and over-provisioning are standard practices used to reduce the number of times any particular memory cell is written to. Also, device and system level error correction schemes are employed to ensure that unrecoverable data losses are minimized.
These mitigation strategies have proven so effective that SSDs now equal or actually outpace HDDs in reliability and longevity. Both now have expected life spans of about six years. Plus, according to a report by the Storage Networking Industry Association (SNIA), SSDs boast a MTBF (Mean Time Between Failures) rate that is more than twice as good as that for HDDs.
4. SSDs Performance Gets Worse Over Time
Flash memory devices are at their fastest fresh out of the box (FOB) due to the fact that SSDs cannot just overwrite previously stored data. Before a location can be written to, any previously existing data in that location must be erased. Since the erasure process takes time, a SSD will exhibit its highest level of performance when there are plenty of never-used blocks available that don’t have to be erased before they can be written to. As the drive fills up, the number of such blocks diminishes, negatively impacting performance.
In the past, some users saw the speed of their drives deteriorate over time because manufacturers rated the product based on FOB specs rather than on “steady state” performance.
Today’s SSD products attack the issue on a couple of fronts. On a technical level, a process called “garbage collection” is employed to pre-erase previously used blocks in the background so they are already available when a write request is received. Also, drives are now routinely overprovisioned beyond their stated capacity to provide more empty space so that fewer erase cycles are required. And finally, published specs now normally reflect the performance that can be expected under actual production conditions, rather than FOB.
5. SSDs Are Only Useful For High Performance Workloads
Adam Roberts, Chief Solutions Architect for SanDisk, writes of the many occasions on which he has heard customers say something like, “I haven’t considered flash for this solution because the HDDs meet my performance needs.” The unspoken assumption behind such statements is that SSDs are important only because of their blazing speed. Well, that speed advantage certainly is important, especially for demanding workloads. But that’s not the only benefit SSDs offer.
Because of the advantages SSDs have over HDDs in storage density and power consumption, their use can reduce the number of drives, servers, and enclosures required. The result is that when costs such as power, cooling, data center floor and rack space, and maintenance are taken into account, the TCO for SSD storage solutions may already be less than that for equivalent HDD implementations. So, even when a company’s applications don’t require the highest levels of storage I/O performance, incorporating SSDs into its storage solution can lower overall costs significantly.
If you’ve been holding back from considering SSD storage because of concerns such as the ones we’ve discussed in this article, maybe it’s time to take another look. We here at Zadara Storage would be happy to help. Please request a customized TCO analysis.
