Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

ddramdisk.store

Post reply on HN
Print view View original

41–50 of 128 posts

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

#41

Post by rsaxvc »

jeroenhd wrote: post #36
remlov wrote: post #29

Earlier quoted context omitted.

ECC is supported, see the following comment: https://ddramdisk.store/2023/01/19/the-ddr4-pcie-x8-lady-has...

That's very good. I'm not sure how the drive would signal bitflips that can't be corrected (and what the operating system will do when it happens), but at least the support is there!

The same way NVMe does, as a failed read?

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

#42

Post by matja »

qwerty456127 wrote: post #37

I wonder why this is not a commonly available and used thing. I have always wanted to use more RAM chips than my CPUs/motherboards would support, put all the swap on RAM chips, probably also load the whole OS&apps system drive into RAM this way (hint for your board: add an SSD it would load from, single-time on turn-on) and only use a persistent storage drive for my actual data files. Using more RAM instead of HDD/SS…

> The amount of RAM you were allowed to plug into a PC motherboard always felt like the most annoying limitation

You could always get motherboards that took more RAM, just not ones that taking your typical gaming CPUs and RGB. Currently there are standard desktop-sized ATX motherboards that take 3TB of DDR5, and ATX boards that take 1TB of DDR4 have existed for years.

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

#45

Post by antisthenes »

qwerty456127 wrote: post #37

I wonder why this is not a commonly available and used thing. I have always wanted to use more RAM chips than my CPUs/motherboards would support, put all the swap on RAM chips, probably also load the whole OS&apps system drive into RAM this way (hint for your board: add an SSD it would load from, single-time on turn-on) and only use a persistent storage drive for my actual data files. Using more RAM instead of HDD/SS…

Because of the price of buying this DDR4 RAM expansion disk for, say, 1TB capacity, it would be cheaper just to buy a proper server board that has 16+ RAM slots and run the RAM-Disk in software?

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

#46

Post by zitterbewegung »

qwerty456127 wrote: post #37

I wonder why this is not a commonly available and used thing. I have always wanted to use more RAM chips than my CPUs/motherboards would support, put all the swap on RAM chips, probably also load the whole OS&apps system drive into RAM this way (hint for your board: add an SSD it would load from, single-time on turn-on) and only use a persistent storage drive for my actual data files. Using more RAM instead of HDD/SS…

You can do something similar (without a LiPo) in software from Linux https://linuxhint.com/create-ramdisk-linux/

The limitations would be the system would need to have a battery backup.

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

#47

Post by crest »

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?

While local NVMe SSD raids can max out a PCIe 16x slot with given large enough blocks and enough queue depth they still can't keep up with small to medium sync writes writes unless you can keep a deep queue filled. Lots of transaction processing workloads require low latency commits which is where flash-backed DRAM can shine. DRAM doesn't requires neither wear leveling nor UNMAP/TRIM. If the power fails you use stored energy to dump the DRAM to flash. On startup you wait for the stored energy level to come to safe operating level while restoring the content from flash, once enough energy is stored you erase enough NAND flash to quickly write a full dump. At this point the device is ready for use. If you overprovision the flash by at least a factor of two you can hide the erase latency and keep the previous snapshot. Additional optimisations e.g. using chunked or indexable compression can reduce the wear on the NAND flash effectively using the flash like a simplified flat compressed log structured file system. I would like such two such cards each of my servers as ZFS intent log please. If their price and capacity are reasonable enough I would like to use them either as L2ARC or for a special allocation class VDEV reserved for metadata and maybe even small block storage for PostgreSQL databases.

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

#48

Post by nubinetwork »

rwmj wrote: post #12
nubinetwork wrote: post #8

Earlier quoted context omitted.

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.

I don't personally, because battery backed SRAM is a poor man's eeprom.

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

#49

Post by lopkeny12ko »

qwerty456127 wrote: post #37

I wonder why this is not a commonly available and used thing. I have always wanted to use more RAM chips than my CPUs/motherboards would support, put all the swap on RAM chips, probably also load the whole OS&apps system drive into RAM this way (hint for your board: add an SSD it would load from, single-time on turn-on) and only use a persistent storage drive for my actual data files. Using more RAM instead of HDD/SS…

Why would you want to put swap on a physical disk that is effectively RAM? That seems like a very redundant solution since swap as a concept becomes irrelevant if both main memory and swap are both volatile and equally fast. At that point, just add more main memory. The kernel is designed explicitly under the assumption that the storage backing swap is orders of magnitude slower.

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

#50

Post by fulafel »

qwerty456127 wrote: post #37

I wonder why this is not a commonly available and used thing. I have always wanted to use more RAM chips than my CPUs/motherboards would support, put all the swap on RAM chips, probably also load the whole OS&apps system drive into RAM this way (hint for your board: add an SSD it would load from, single-time on turn-on) and only use a persistent storage drive for my actual data files. Using more RAM instead of HDD/SS…

How much do you need? I think you can put 8 TB now.

(And of course you get a lot better bandwidth and latency than hanging it off some IO attachment)

Post reply on HN