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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

#61

Post by PragmaticPulp »

hyperific wrote: post #17

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.

> From image capture at the microscope to segmentation and some post processing steps the biggest bottleneck for us is disk speed.

If you're doing sequential writes, this drive benchmarks slightly slower than the fastest PCIe 4 NVMe drives on the market.

Upcoming PCIe 5 NVMe drives will be significantly faster than this.

This unit is really only helpful for extremely small random writes or if you're doing so much writing that you exhaust the wear capacity of a normal SSD.

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

#62

Post by Dylan16807 »

Felger wrote: post #7
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?

A very useful use case discovered no later than last week : local dedup management by Synology C2 Backup Agent and TBW on the OS SSD. C2 Backup agent stores dedup/chunks data by default in ProgramData, which is stored on C:... which is usually a SSD nowadays. I noticed a 3:4 ratio between written data in local dedup folder vs uploaded data volume on the remote C2 5 TB storage (suscribed a C2 Business). TBW grew indee…

I think the question was more tuned to physical ram disks, but I'm not sure.

Either way, how many terabytes were being written each day? And how much can your drive take? It looks like I could go pay $60 right now for 600TB of endurance, and $35 for 200TB of endurance. If you already have the extra ram than go for it but it doesn't seem like a setup to make on purpose.

Maybe your backup system has far more writes than mine? I have terabytes of backups but the average written for each daily backup is about 10GB.

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

#63

Post by PragmaticPulp »

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…

> 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.

You could create a RAM disk post-boot and then copy apps into it or use it for a working directory.

But you'll be disappointed to discover that virtually nothing benefits from this compared to a modern SSD. Copying files will be faster, but that's about it.

Operating systems are already very good at caching data to RAM. Modern SSDs are fast enough to not be the bottleneck in most operations, from app loading to common productivity tasks.

Even when we all had slower HDDs in our systems, creating a ram disk wasn't a big enough improvement to warrant creating a ram disk for most tasks. I remember reading a lot of experiments where people made RAM disks to try to speed up their development workflows, only to discover that it made no different because storage wasn't the bottleneck.

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

#64

Post by cryptonector »

PragmaticPulp wrote: post #56

Interesting design. They use FPGAs to emulate NAND storage with DDR, then use a standard NAND SSD controller. It doesn't perform any better than fast NVMe SSDs for larger, sequential operations. However, it appears to be an order of magnitude faster for the random 1K read/write operations. It also has infinite durability relative to an SSD, though obviously your data isn't infinitely durable during a power outage sce…

But it must suffer from rowhammer.

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

#65

Post by JonChesterfield »

PragmaticPulp wrote: post #58
JonChesterfield wrote: post #54

An interesting quirk of the later designs is they're bring your own ram. That might be a worthwhile thing to do with a pile of DDR3 from an old server. I think I've got 256gb or so in a draw somewhere that's otherwise unlikely to see any use. Lithium battery strapped to consumer chips - so you can basically ignore the volatility aspect (possibly in exchange for an exciting new fire risk, not sure how professionally b…

> An interesting quirk of the later designs is they're bring your own ram. That might be a worthwhile thing to do with a pile of DDR3 from an old server. I think I've got 256gb or so in a draw somewhere that's otherwise unlikely to see any use. The 256GB version is listed at $280. That's more than enough to buy the fastest 2TB SSDs on the market which will match the performance of this device for most real-world work…

That's the previous version with memory soldered on. There's no price listed for the one with DIMM slots.

However it turns out I was way out of date on nvme pricing. So that's awesome, if fairly bad news for this product.

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

#67

Post by cronix »

I remember doing something similar in windows 3.1 back around 90-91. Hard disks weren't quite fast enough to play very good video (I was using 3D Studio back then and IIRC this was still owned by Autodesk then as a spinoff product of Autocad) so you made a ramdisk and played the video from that. Only a few seconds at 640x480x256(colors) though. I think I had 4 Megs of ram in that 486 machine.

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

#68

Post by sandworm101 »

PragmaticPulp wrote: post #56

Interesting design. They use FPGAs to emulate NAND storage with DDR, then use a standard NAND SSD controller. It doesn't perform any better than fast NVMe SSDs for larger, sequential operations. However, it appears to be an order of magnitude faster for the random 1K read/write operations. It also has infinite durability relative to an SSD, though obviously your data isn't infinitely durable during a power outage sce…

>> infinite durability relative to an SSD

Until the FPGA dies. Consumer-grade arrays are not eternal. Many have lifespans (>5% failure rate) as low as 2-5 years under regular use.

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

#69

Post by peter_d_sherman »

I like the idea of using multiple FPGAs to ["fanout"/"cascade"/"distribute"/"one-to-many proxy" -- choose the terminology you like best] the SM2262EN to multiple sticks of DDR3 RAM...

I'd be curious though, if the SM2262EN itself couldn't be replaced by yet another FPGA, and, if so, if the FPGA used for that purpose could be the exact same type as the other four...

If so -- then one could sort of think of that arrangement as sort of like a Tree Data Structure -- that is 2 levels deep...

But what would happen if we could make it 3 or more levels deep?

?

In other words, if we had 4 such boards and we wanted to chain them -- then we'd need another central memory controller (another FPGA ideally) -- to act as the central hub in that hierarchy...

It would be interesting, I think, to think of a future hardware architecture which allows theoretically infinite upscaling via adding more nested sub-levels/sub-components/"sub-trees" (subject to space and power and max signal path lengths and other physical constraints, of course...)

I also like the idea of an FPGA proxy between a memory controller and RAM... (what other possibilities could emerge from this?)

Anyway, an interesting device!

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

#70

Post by mittermayr »

PragmaticPulp wrote: post #56

Interesting design. They use FPGAs to emulate NAND storage with DDR, then use a standard NAND SSD controller. It doesn't perform any better than fast NVMe SSDs for larger, sequential operations. However, it appears to be an order of magnitude faster for the random 1K read/write operations. It also has infinite durability relative to an SSD, though obviously your data isn't infinitely durable during a power outage sce…

Would be interesting if there would be a case for slapping an SSD on the back of it and giving it just enough capacitor power to dump whatever is on RAM to the SSD once a power-out happens (and restore upon boot). SSD writes would be super low (rarely) and only happen during power issues or shutting it all down.
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