using ram as storage

ynnHvHyt · June 25, 2020

this is a dumb idea, but dumb enough to work? i was looking into it and although a costly solution that would wipe after a power down is there some possible way to use ram as storage.

Master Disaster · June 25, 2020

Its called a RAM Disk, its been a thing since at least the 90s.

Stahlmann · June 25, 2020

Linus did a video about this some time ago on LTT. That's actually a thing.

Kisai · June 25, 2020

49 minutes ago, ynnHvHyt said:

this is a dumb idea, but dumb enough to work? i was looking into it and although a costly solution that would wipe after a power down is there some possible way to use ram as storage.

RAM disks are a thing, but they're usually pointless without having the bandwidth.

So for example, DDR2 memory has 4.6GB/sec transfer, but SATAIII has only 0.5GB/sec transfer, so you're basically wasting 88% of the bandwidth. Now if you could connect old DDR2 modules up to a PCIe3.0 M2 slot, PCIE 3.0 at 4 lanes (the same as an NVMe drive) is 4000MB/sec, so you would only be wasting 14% of the bandwidth. The other obvious problem here is that DDR2 modules only went up to 4GB. So you would likely need 128GB to fit the largest games if you really wanted to do this, and by that point you're just making things too difficult.

So let's move on to DDR4. The cheapest, lowend DDR4 memory is DDR4-1600 with 12.8GB/sec transfer. So to put this on the secondary storage side of a PC, you would need at least 12 PCIe 3.0 lanes or 6 PCIe 4.0 lanes to get there. So let's assume we have a mythological DDR4 ramdisk using reclaimed DDR4-1600 modules from old Skylake systems. If you run it all as a single channel, 128GB could be assembled rather easily with 16 sticks of 8GB, but it would be even easier to assemble using 8 sticks of 16GB modules. This is still over complicated and also hasn't covered the other problems.

Dual channel, Quad channel, Triple channel? Why limit ourselves to one channel for any reason than it being wasted. So as I just mentioned, 12 PCI 3.0 lanes in single channel mode, but what if we ran it in dual channel? you'd need 24 lanes 3.0 lanes or 12 4.0 lanes. What about triple channel? 36 3.0 lanes or 16 4.0 lanes. There's the number we want to see. So let's say we put a triple-channel ramdisk on a 16 lane card instead of a 16 lane GPU.

Now you also need some NVMe to DDR4 translation chip, and a BBU (Battery Backup Unit)

So what is the end result? I couldn't find anyone selling this memory, particularly as a 128GB set, so I'm just going to guess using the DDR4-2333 memory at $125 per 32GB. So $500USD for a 128GB drive when you could spend the same amount and get a Samsung 2TB EVO 970 Plus NVMe drive for $480, and that wouldn't involve inventing a DDR4 ramdisk controller.

Now, before we get ahead of ourselves. There are some MB's that let you create a ramdisk as well. Below is a Frost Canyon NUC Intel board.