What Solid State Storage Form Factor Is Best?

Solid state storage comes in several form factors. Each has its value to both suppliers and to users of the technology. In the data center there seems to be three popular choices emerging; solid state disk drives, PCIe solid state cards and solid state appliances or memory arrays. Choosing the right one for your environment is critical in making sure that you get the most out of your solid state investment.At the Flash Memory Summit last week (see our briefing notes here) there was at lot of progress on all fronts; faster and smaller solid state drives, higher capacity PCIe solid state cards and more scalable solid state appliances. What struck me is how is a user to determine which type of solid state storage is best for their environment? Over the next few entries we will look at each of the types of solid state storage and give some ideas on when each might be best for the user. You can also check out our webcast on the State Of Solid State Storage 2010 for more details on each.

The first card type we will examine is the PCIe solid state card. This is a card that installs inside of a server. Being PCIe based gives the board more power than the standard solid state drive style of device which allows it to power more flash cells. Being PCIe based also gives the CPU the purest access to the solid state disk than any of the other connection types. This means that PCIe based systems have fewer bottlenecks to contend with.

The downside to the card is that while there is more capacity per card available there is a limit to how many cards you can install into a system. They are ideal for 500GB performance problems, not 2TB performance problems. The also require operating system drivers in order to work. If you are running Windows you are probably safe, any other OS can be hit or miss. Installing PCIe SSD is also typically a disruptive upgrade. You'll have to power down the server, install the drivers for the PCIe card and reboot the server. Finally you can not boot from PCIe solid state storage. So these cards are ideal for cache areas, or for a storage location for swap and database temp files. Of course the size is such that in many cases the entire database can fit on the card.

Where PCI solid state can be very compelling is as less expensive RAM instead of thinking of them as storage. RAM is expensive, you usually buy more to increase the cache area that a database can use before having to resort to accessing the information on spinning storage. Since PCIe is so fast it can act as slow RAM with one key advantage, it is persistent. Data lost in cache when a server crashes is data that is lost forever. Data storage on a flash PCIe card when a server goes down is still there when the server comes back up. The objective with this configuration is to lower the amount of RAM installed in the server and lower the amount of cache that your application is allocated and then redirect that area to storage, just have that be the PCIe based storage.

PCIe solid state provides cost effective high performance storage without the bottleneck concerns of other solid state form factors. PCIe has its place in the infrastructure, and it shouldn't surprise you to expect to see PCIe solid state used in conjunction with other solid state devices; they may not always be competitive to the other forms of solid state storage. In our next entry in this series we will cover the drive form factor of solid state disk.

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George Crump is lead analyst of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. Find Storage Switzerland's disclosure statement here.