Putting flash in the application server is becoming the performance solution of choice, but how do you choose which type of flash to use? Let’s start by taking a look at the different types of SSDs available for use in the server.
Drive form-factor SSDs
These were the original SSDs, essentially plug-replacements for 2.5” hard drives. As you can imagine using drive form-factor SSDs for boot drives is one of the most popular applications of this drive type. Since they’re also the least expensive, on a $/GB basis, these SSDs are often used when higher capacities are needed. Performance is the lowest of the three SSD types discussed here, since they’re limited by the speed of the SAS/SATA connection.
PCIe form-factor SSDs
These devices pack flash chips on PCIe cards which are installed inside the server. These cards are much more sophisticated (and more expensive) than drive form-factor SSDs and offer better performance as well. With the added real estate available, PCIe SSDs can have multiple flash controllers embedded on them and can also support caching software.
Applications for these products include caching, with software that’s onboard the PCIe card or running in the server CPU, and tiering where the software typically runs in the server. Another use case that’s gaining popularity is virtual memory expansion. Since PCIe cards have relatively low latency, they can provide flash as ‘slow memory’ storage instead of the more traditional ‘fast hard drive’ storage. The ability to expand effective memory in this way is a big enabler of increased VM density, and a way to save significant cost.
DIMM form-factor SSDs
Flash is now also being put on the same dual in-line package cards that hold DRAM and connect to the computer mother board. Putting flash on the memory bus like this is the lowest latency method currently available and is ideal for the virtual memory expansion use case mentioned above. DIMM slots are often more available in low-profile servers as well, making this form factor a good way to add flash capacity when drive slots and PCIe slots are in short supply.
In the webinar “Three Keys to Choosing the Right Server Flash” we go into each of these SSD types and talk about how they’re being used in more detail.
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