IntelMemory Drive Technology

[ChuffyD]

Has anyone tried using Intel memory drive technology (imdt). It allows you to extend DRAM by using an Optane drive. The driver does this without the applications knowledge (no code change necessary) and from what I can tell it will page memory to the Optane drive. It works with 900/905p and p4800x/p4801x.

As the Optane drive will be used for non persistent storage I don’t think you need the features of the 480xxx. A 905p is coming out around half the price of DRAM.

My thinking is this would replace the need for L2ARC (assuming a need due to the workload) and would be more efficient as there wouldn’t need to be a lookup table in DRAM. Appreciate it would still be orders of magnitude slower than DRAM, but if may allow you to get the full working data set into ARC at a lower price.

 

[Rand]

And you're going to install the needed software how on your TrueNas Core box?

 

[HoneyBadger]

Ignoring the fact that there's no FreeBSD support, because TrueNAS might one day be Linux-based even outside of SCALE ...

While FreeBSD has some rudimentary support for persistent memory devices, ZFS hasn't been updated to take full advantage of them as byte-addressable persistent devices, and still has to go through the block layer to address them as L2ARC.

The Intel Memory Drive Technology (IMDT) integration is basically just replacing the L2ARC (which ZFS has knowledge and manageability of) with some proprietary black-box Intel technology, since it's letting the IMDT driver/shim handle what's in actual RAM vs on an Optane SSD - I'd be worried that IMDT would do something silly like "page out" kernel or ARC metadata/headers.

[this] would be more efficient [than L2ARC] as there wouldn’t need to be a lookup table in DRAM.

You're just replacing the ZFS L2ARC headers with the IMDT PMEM headers. Whether they're more efficient or not, I'm uncertain; but L2ARC headers are 88 bytes per record I believe, is now persistent, and I'll take the known capabilities to tune and integrate them over trusting Intel's black-box.

Proper support for pmem devices in ZFS would be lovely, but I'd rather see the effort focused on enabling "byte addressable SLOG on NVDIMM" first because a memcpy() beats the hell out of going through a memory-mapping storage driver just to loop back to a DIMM.

(TL;DR no, but one day we'll be able to, and it will be pretty sweet if you can afford Optane DC DIMMs.)