Placing SSD in the server is a popular option, especially if only a small percentage of your servers are having a performance problem. It allows a surgical, performance strike on the server giving you the most grief. It also puts the high-speed storage closer to the processor and removes the shared storage network as a potential bottleneck. There are typically three SSD form factors; the hard-drive form factor SSD, SSD DIMM, and PCIe SSD.
Hard-drive form factor SSDs looks and acts like a mechanical hard drive, just with no spinning media in them. They were one of the first SSD implementation forms commonly available. They made for the ideal hard drive upgrade. Install the drive form factor SSD, copy your data over, and reboot for an easy speed boost.
Hard-drive form factor SSDs are now joined by SSD DIMM, as we discussed in our recent article "SSD DIMM - An Alternative to PCIe SSD," as devices that can be installed in your server's DIMM slots and act exactly like mechanical hard drives, connecting to the system connect via standard SAS or SATA interfaces. This type of connection makes both of these form factors ideal boot devices. They are limited to the connection speed of the interface, but for many environments that's all the performance boost that's needed.
PCIe SSDs are the other server SSD option and are rapidly gaining in popularity. As the name suggests these SSDs connect via the PCIe bus and, as a result, have direct access to the CPU via a high-speed channel, which provides a very high-performance option. While most PCIes can't be booted from, they are ideal for extremely high-performance workloads where even the bandwidth of SAS/SATA is not enough for the performance requirements of the application.
PCIe SSD can also be used as a low-cost DRAM memory option. Instead of paying to load a server up with 100s of GBs of DRAM, a 1-TB SSD area, acting as memory, can be purchased to provide more broad-based acceleration.
Which server based SSD you will use depends on what the performance problem is and the realities of what can be installed in that server. Many PCIe SSD cards require a full size PCIe slot, something that most 1U and 2U servers do not have. In these situations, a hard-drive form factor or SSD DIMM is the better--or even only--alternative, depending on if there are drive or DIMM slots available.
Server-based SSDs can be used for a variety of purposes and can still complement and enhance a shared storage infrastructure, not replace it. In our next entry we will look at some of the more ideal use cases including booting, caching, swap space, and using SSDs instead of DRAM memory.
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