What To Look For In PCIe SSD

At the Flash Memory Summit last week, PCIe SSD went from a niche category to a competitive market. In the last year this market has grown from two companies in the category to at least six today. The problem is that to a large degree all PCIe SSD look basically the same, so how are users supposed to select the right PCIe SSD for their needs?

For the purposes of this entry we will assume that you have done your homework and determined that your application or environment could indeed benefit from solid-state storage. If you haven't, we wrote a visual step by step guide that may help. In general, almost any environment that is not CPU bound will see a performance gain by switching to solid-state drives (SSDs). The analysis phase gives you a feel for how much of a performance difference you will witness and how much SSD you should use.

The next point to determine is if SSD in the server, regardless of type, is what you need versus shared SSD. In general, if a small percentage of your server population has a storage performance problem and data between those servers does not need to be simultaneously shared, then there is potentially a good fit for server-side SSD. Additionally, the line between server-based solid state and shared solid state will get increasingly blurry as technologies like caching and tiering continue to take hold (more on that in a future entry).

Once the "will it benefit you" analysis is done it is time to move on to trying to decide on a particular PCIe SSD. There is no particular order to the qualifiers, and you'll need to give each one its own weight in importance. The easiest qualifier and one that makes sense to address upfront is "will it fit?"

Initially many of the PCIe SSD cards were full sized and simply won't fit into smaller servers. There are now several choices of cards that are smaller and will fit into tighter spaces. Make sure you clarify the size of the card and how much space you have in your server. The lack of available PCIe slots, especially in 1U servers, may be the biggest reason not to choose PCIe SSD. If space can't be made, then you are going to need to look at drive form factor SSDs or the new SATA DIMM SSDs that can be installed in a memory DIMM slot.

Another type of resource consumption to consider is how the PCIe card uses other server resources like CPU and RAM. There is a large debate among the PCIe SSD vendors as to the consumption of host resources and if it matters or not. Some PCIe SSDs use the server's CPU and memory to help it manage the Flash NAND. In some cases this can be 5% of the CPU resource and 1 GB of RAM per PCIe card. Other PCIe vendors use very little to no server resources. How important this is to you will depend in large part how much of those resources you have available and how predictable you need performance to be under load.

Once you know that the PCIe SSD will fit into your servers and understand the resources requirement, the next step is to understand what you are going to use it for. How to best use PCIe SSD in your environment will be the subject of our next entry.

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