The early choice for server-side SSD, as for shared storage, was to use drive form-factor SSDs. These SSDs look like hard disk drives (HDDs) but contain solid-state memory instead of rotating media. They installed into a conventional HDD expansion bay, so support and installation was easy.
Drive form-factor SSDs gave way in large part to PCIe SSDs, which are PCIe boards with flash modules installed. PCIe SSD provided a performance advantage over drive form-factor SSD thanks to their direct connectivity to the PCIe bus and avoidance of the storage protocol stack. But PCIe SSDs have their own challenges. First, because they avoid the storage protocol stack, they require a customized driver and you can't boot from them. This means not all platforms are supported by every vendor, requiring at least two types of drives in the server -- typically HDD to boot and PCIe SSD for performance.
Second, PCIe SSDs have a redundancy problem. Most servers don't have an abundance of free PCIe slots. Even if it is supported, installing multiple cards can be a challenge. Without multiple cards it's difficult to develop mirroring or RAID capability -- and for most servers, hot-swapping PCIe cards is out of the question.
[ Server-side storage memory can offer a cost-effective solution to VDI projects. Here's how: How Server-Side Storage Memory Impacts VDI Costs. ]
Drive form-factor SSDs don't have these challenges. A good number of drive bays are usually available, and these drives can leverage the redundancy options built into the RAID controller they connect to. As discussed in this webinar, the comeback of drive form-factor SSD is being driven by improvements in performance and smaller form factors, which leads to greater density.
6-GB (and soon 12-GB) SAS and SATA protocols can overcome much of the performance bottleneck. As discussed here, even 6-GB SATA is achieving 600+ MB performance per drive. With the appropriate RAID controller capable of driving a server full of these drives, 200k+ IOPS is very achievable. In addition, SSD manufacturers have been making great strides in performance and durability.
Improvements in storage protocol performance, RAID controller processing power and in the devices themselves should encourage enterprises looking for server-side SSD to give drive form-factor technology a fresh look. Add in their easy availability, and these devices make a compelling case for companies looking to improve server-side performance.
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