Take Five With Tom Fenton
5 Tips for Selecting the Right NVMe Devices
These storage devices are great, but it's not a simple matter of plug-and-play.
NVMe devices are currently the most performant commodity storage devices available for datacenters. They're not inexpensive, but their high bandwidth and low latency can supercharge applications running in a physical or virtual environment.
NVMe devices are quicker than SSD and HDD drives, but each device will have unique characteristics that must be taken into account when choosing which one to use in your datacenter. Here's a list of five characteristics you should examine to make sure you select the NVMe device that most closely suits the needs of your datacenter.
- Form factor. NVMe devices come in three form factors: M.2, U.2, and half height, half length (HHHL). HHHL devices plug directly into PCIe slots, and U.2 devices require a special slot on your server's motherboard. Both of these form factors require opening a server's case for servicing. U.2 devices look like 2.5 inch SSD drives and can be hot-swapped in and out of a drive bay if it's supported by the server's hardware and OS.
- Match it to your infrastructure. The latency and bandwidth of NVMe devices is outstanding, but you need to make sure that the server on which they will reside will be able to handle it. Not only should your server support the speed of the NVMe drive, it should also support the number of drives that you want to run on it, and at that speed.
- Compatible read/write characteristics. Because all NVMe devices have unique read and write characteristics, some are better at writes and some at reads. Since the type of memory or cells that they use has a significant impact on the device, make sure to choose an NVMe device with the right type of memory technology for your workload.
- Device longevity. NVMe devices are only good for a certain amount of write cycles, and most devices are rated according to how many terabytes can be written to them before they start to become unreliable. A device's longevity may be expressed in writes per day or in total terabytes that can be written to it. From what I have seen, most of the major suppliers' NVMe devices have been very conservative with their lifespan estimates.
- Price. The actual price of the drive is not a simple calculation of dollars per gigabyte. All the previous factors must be weighed to get the true price of a device. For example, it may be more cost effective in your case to select a lower performing device over a higher performing device if your server can't take advantage of the performance of the higher performing device.
Moreover, it may be tempting to go with an NVMe device with a long life, but the reality is that it might be wiser to go with a less expensive device with a lower longevity. Between server refreshes and the price drop in NVMe devices, a less expensive device may not wear out before its useful life is served, or it may simply be cheaper to replace it in the future than pay a premium for a device with a longer lifecycle.
As one last piece of advice: once you get to the point of benchmarking an NVMe device, be sure to first precondition the device with at least one write to each memory location on the entire device. This is because the first write will be considerably faster than subsequent writes on most devices.
Tom Fenton has a wealth of hands-on IT experience gained over the past 25 years in a variety of technologies, with the past 15 years focusing on virtualization and storage. He previously worked at VMware as a Senior Course Developer, Solutions Engineer, and in the Competitive Marketing group. He has also worked as a Senior Validation Engineer with The Taneja Group, where he headed the Validation Service Lab and was instrumental in starting up its vSphere Virtual Volumes practice. He's on Twitter @vDoppler.