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Are Solid State Disk Storage Options Right for Your Enterprise?

When weighing the benefits of the newest player in the storage market, enterprises need to look at the increased performance vs. the relatively small storage size.

• By Scott D. Lowe
• 05/07/2013

Solid state disks based on flash storage are all the rage these days. Companies scramble to integrate bleeding edge technology into their company portfolios in order to jump ahead of the curve in capitalizing on new trends. Flash storage is rising in popularity due to its sheer speed; it outpaces a traditional hard drive by orders of magnitude.  These massive performance gains enable consumers to get things done faster since they're not waiting on storage.  Further, they enables organizations to consider new business opportunities that may not have been otherwise feasible, such as crunching big data figures in search of revenue.  From a pure performance perspective, solid state disks are pretty inexpensive.

These newest players on the market remain a mystery to many people, though.  In fact, solid state storage is radically different from traditional hard disk-based storage.  About the only commonality between a solid state disk and a hard disk is the SATA or SAS connector on the back that plugs the device into the system.

On the flip side of the equation, solid state disks are pretty terrible when it comes to raw capacity.  Traditional spinning hard drives can grow to be much larger than solid state disks.  It's common to see solid state disks still measured in gigabytes, whereas the biggest traditional hard disk tops out at a whopping 4 TB.  In terms of capacity, then, solid state disks are very expensive.

Over the years, hard drives have become pretty well known technology.  Most technology pros are aware that certain types of disks are generally better than certain other types.  For example, did you know that a typical SAS disk is an order or magnitude more reliable than a typical SATA disk?  An Unrecoverable Read Error (also known as the Bit Error Rate) -- an event that can be catastrophic in the wrong scenario --  is 1 in 10^14, meaning that, on average, an unrecoverable read error will take place every 12.5 TB (8 bits per byte).  SAS disks, on the other hand, carry an unrecoverable read error ratio of 1 in 10^15, meaning that, on average, it takes 125 TB for such an event to occur.  Bear in mind that some enterprise-grade SATA disks may have 1 in 10^15 URE figures, too; check your packaging.  Also, if you're hoping to capitalize on cheap near line SAS (NL-SAS) disks for capacity and want SAS' reliability, don't use NL-SAS!  NL-SAS disks are usually SATA disk parts coupled with SAS connectors.

Unrecoverable Read Errors have become a real problem as the size of hard drives has grown.  With drives into the terabytes, the risk of running into a URE during a RAID 5 rebuild is higher than most people would like to consider.  In such a situation, the storage array would suffer a double disk fault, which would more than likely not only lead to a serious data loss event but also impose significant downtime.

Solid state disks, being newer, aren't as well understood as their spinning counterparts.  First off, solid state disks have no moving parts.  This both increases their operational reliability and removes some physical roadblocks from the performance side.

There are a couple of different kinds of solid state disks (SSDs) available out there:

• Single level cell (SLC).  SLC SSDs are the most reliable, the fastest and the most expensive of the bunch.  With SLC SSDs, you're able to store one value per single cell. Further, the cell value can be just one of two states.  Because of this single layering and the simple yes/no nature of SLC, it's very fast and very robust.  SLC SSDs are used in the highest-end applications that demand the fastest speeds.  For example, a very high-end business intelligence platform might need this kind of speed for number crunching.  SLC SSDs are also more tolerant to poor operating conditions, such as harsh weather, and have more endurance than MLC SSDs.
• Multilevel cell (MLC).  MLC SSDs are still really fast, but they're a bit less expensive than their SLC counterparts.  With MLC disks, each cell can be in one of four different states.  While it's possible to store more data on an MLC SSD, MLC isn't quite as fast as SLC, since the storage has to take more time to determine a cell's state. MLC SSDs are less expensive than SLCs and have greater capacity than SLCs but not as much capacity as modern hard drives.

Although the world is beginning to shift toward more and more use of solid state disks, from a pure capacity standpoint, nothing yet beats hard drives.  Even there, administrators must take care to ensure that the disks they choose carry the performance and reliability characteristics they need.