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DDRamDisk: RAM disk, a disk based on RAM memory chips

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Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#11

Post by Dalewyn »

GordonS wrote: post #2

I don't have a use for this, but I enjoyed the detailed write-up! In these days of fast SSDs, are there still uses for a RAM disk, beyond extreme niches?

SSDs currently peak somewhere around 7GB/s transfer speeds, while RAM can easily knock out well over 20GB/s (and that's a low estimate). So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk.

SSDs are also consumable, as mentioned in other comments, so RAM disks are perfect for a scratch disk. HDDs can also serve as a scratch disk, but some tasks also appreciate the aforementioned faster transfer speeds and/or lower latency of SSDs or RAM.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#12

Post by rwmj »

nubinetwork wrote: post #8
sandworm101 wrote: post #3

Not a new concept. Has been done a few times before. The use cases are very small, and getting smaller these days as motherboards accept larger and larger memory modules. https://www.newegg.ca/gigabyte-gc-ramdisk-others/p/N82E16815...

Even older... https://silentpcreview.com/review-blast-off-with-cenateks-ro...

The concept is old as the hills, if you include static RAM. It was a common way for early digital synthesizers (early 80s) to store patches in battery backed SRAM. Even on removable cards.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#13

Post by rwmj »

GordonS wrote: post #2

I don't have a use for this, but I enjoyed the detailed write-up! In these days of fast SSDs, are there still uses for a RAM disk, beyond extreme niches?

We used a network-backed temporary RAM disk for use in our RISC-V package build system. Each time a build is started it connected to the NBD server which automatically created a RAM disk ("remote tmpfs"). On disconnection the RAM disk was thrown away. Which is fine for builders, I wouldn't much recommend it for anything else! https://rwmj.wordpress.com/2020/03/21/new-nbdkit-remote-tmpf...

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#14

Post by GordonS »

Dalewyn wrote: post #11
GordonS wrote: post #2

I don't have a use for this, but I enjoyed the detailed write-up! In these days of fast SSDs, are there still uses for a RAM disk, beyond extreme niches?

SSDs currently peak somewhere around 7GB/s transfer speeds, while RAM can easily knock out well over 20GB/s (and that's a low estimate). So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk. SSDs are also consumable, as mentioned in other comments, so RAM disks are perfect for a scratch disk. HDDs can also serve as a scratch disk, but some tasks also appreciate the aforeme…

> So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk

Well, anything that doesn't require persistence!

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#15

Post by mxfh »

Dalewyn wrote: post #11
GordonS wrote: post #2

I don't have a use for this, but I enjoyed the detailed write-up! In these days of fast SSDs, are there still uses for a RAM disk, beyond extreme niches?

SSDs currently peak somewhere around 7GB/s transfer speeds, while RAM can easily knock out well over 20GB/s (and that's a low estimate). So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk. SSDs are also consumable, as mentioned in other comments, so RAM disks are perfect for a scratch disk. HDDs can also serve as a scratch disk, but some tasks also appreciate the aforeme…

You can easily get to about 20 GB/s by using PCI-E 4.0 NVMe in striped 4x configurations. Comparing this 16x setup to single lane SSD access is not a fitting comparison. With prices for NVME finally going down, you can get 8TB at those speeds for under USD 1k.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#16

Post by vertnerd »

I worked on a PC/DOS based instrument for testing permanent magnets back in the 80s. Because of all the magnets involved, we used a battery-backed Static RAM disk instead of a conventional hard drive. The "disk" consisted of a cartridge that plugged into an ISA expansion card in the PC. It was crazy expensive if I remember correctly. One of my contributions to the project was demonstrating that a conventional hard drive inside a steel computer case was actually quite invulnerable to the stray magnetic fields that we were working with. We could forgo the extra cost of the SRAM disk.

We also used a crazy expensive plasma display for the monitor, which turned out to be overkill. But that's a story for another time.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#17

Post by hyperific »

Where I work we handle massive nd2 time series images often reaching hundreds of GB. From image capture at the microscope to segmentation and some post processing steps the biggest bottleneck for us is disk speed. I'd be very interested to see how fast our pipeline is with one of these at our disposal.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#18

Post by chronogram »

GordonS wrote: post #14
Dalewyn wrote: post #11

Earlier quoted context omitted.

SSDs currently peak somewhere around 7GB/s transfer speeds, while RAM can easily knock out well over 20GB/s (and that's a low estimate). So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk. SSDs are also consumable, as mentioned in other comments, so RAM disks are perfect for a scratch disk. HDDs can also serve as a scratch disk, but some tasks also appreciate the aforeme…

> So anything that benefits from fast transfer speeds and/or low latency will appreciate a RAM disk Well, anything that doesn't require persistence!

All the products like this that I've seen carry a battery for persistence during power outages.

Re: DDRamDisk: RAM disk, a disk based on RAM memory chips

#19

Post by fmajid »

Back when we used something called the DDRdrive X1 as the ZFS ZIL drive (essentially a write log) on our high-performance database machines. It's a PCIe card with 4GB of RAM, 4GB of SLC flash and a supercap so that in the event of a power failure the RAM is written out to flash.

https://ddrdrive.com/menu1.html

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