At last week’s Open Compute Project world summit, Seagate showcased a mechanical hard drive with an NVMe interface – an interface normally reserved for SSDs. The clue is right there in the name: NVM, Non-Volatile Memory. So the first question is … why?
Well, a supposed reason is speed. While Seagate has been promising multi-actuator hard drives for about four years now, you still can’t buy them.
The idea is that by having two (or more) separate arms that come and go independently on the carrier, hard drives can run fast enough that current SATA interfaces prove to be a bottleneck. That’s 6 Gb / s for SATA revision 3, or 600MB / s actually, while NVMe peaks at 20Gb / s.
We suspect that the main reason is money, but there are two aspects to this. It’s not that NVMe is cheaper in itself. First off, while you can buy basic 4TB SSDs now, a cheap SSD still costs around £ 300 and they easily go up to double. This kind of wonga will buy you 18TB of spinning disk. In other words, comparing the price per storage unit, the string rust is still less than a quarter of the price of flash media.
The second factor is that shipping mechanical disks with an NVMe interface will allow vendors to ship servers with only that interface from now on, simplifying the design, which means lower costs. Overall, NVMe hard drives with multiple actuators therefore offer a lower TCO, according to Seagate.
It looks like these devices are set to ship to some customers in 2022, it seems.
There is still room for significant changes in storage space. Intel’s Xpoint 3D persistent memory technology holds great promise, although it is currently struggling in the market. This quality of non-volatile memory can literally be used as memory – it can be inserted into a server’s DIMM slots, rendering external interfaces such as NVMe obsolete. But there will always be a need for slower, high-capacity storage, which in the short term means hard drives.
Having large amounts of non-volatile main memory eliminates many of the current operating system design axioms, and the research barely started, before vendors even got cold feet. But it will come [PDF]. Watch this place. ®