Nice respin on an old theme. Reminds me of the Sun Prestoserve card: https://docs.oracle.com/cd/E19620-01/805-4448/6j47cnj0t/inde...
DDRamDisk: RAM disk, a disk based on RAM memory chips
101–110 of 128 posts
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#102I've really wanted something like that where I could just drop my old RAM sticks and use it as swap space. It would be much better than flash-based solutions, both latency and endurance-wise, probably even over an USB link (3.1 and above speeds are pretty decent, even 3.0 would be enough for basic swap). Bonus points for a DIMM slot that just accepts any generation (DDR2,3,4, not sure if that would be mechanically po…
It wouldn't be mechanically possible to support multiple generations[1]. That's not the only issue with mixing generations.
There are also some interesting electrical engineering problems around driving the bus as you add more SIMMs; probably need multiple CPLD/FPGA memory controllers beyond a certain point. Clocking gets interesting as well. Not impossible, just complicated for an amateur; I know I have problems getting thing to work reliably over 33MHz or so.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#103Earlier quoted context omitted.
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.
My first encounter with the concept was in 1982 during the summer working at an electronics company. We used the then new 64K DRAMs in production so there was a ready supply of devices vendors had given us for evaluation. I built a 128KB memory board with bank selection logic then wrote a driver for the Flex OS (6809) to make that memory appear like a disk. Also built a similar board with (probably, long time ago..)…
If you like FlexOS you'll like this Youtube channel: https://www.youtube.com/user/deramp5113/videos
As for me it's a bit before my time. I started out writing device drivers for Microware OS-9 on 68k.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#104I 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 arrang…
You can implement an SSD controller in an FPGA. That's how all the early server SSDs were implemented. I think my Fusion ioScale was one of them.
It's just an enormous amount of effort. This already looks like a huge amount of engineering to do for what must be a very niche product.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#105Interesting 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 helpful to know how long that battery can keep it backed up.
They say: It has a built-in LiPo and stores your data for up to a year.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#106An 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…
> 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 built these things are) Do LiFePO4 instead. Nothing is fireproof but those are pretty tame.
> Do LiFePO4 instead. Nothing is fireproof but those are pretty tame.
The reason LiFePO4 is safer than higher voltage Liion is because it has less energy per volume. But even LiFePO4 can catch fire if punctured.[1] Although often incorrectly claimed to be, LiFePO4 secondary cells are not "intrinsically safe," like NiMH secondary cells are.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#107Since AmigaOS 1.3 (1987), Amiga has had a software version of a block device in memory which survives reboot, called "ramdrive.device", and usually mounted on DOS as "RAD:". It can even be a bootable device.
This is in addition to the, available since earlier, "Ram-Handler", a filesystem similar to Linux's ramfs, which does not survive reboots.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#108Interesting 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.
Any references on this? Googling didn't let me believe this. From my interpretation (maybe wrong) of Xilinx UG116, FPGAs are reliable.
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#109RAM disks are an old and well-established concept. I'm not clear on what this 'product' adds to them.
https://en.wikipedia.org/wiki/RAM_drive
Re: DDRamDisk: RAM disk, a disk based on RAM memory chips
#110Interesting 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…
Speaking of durability, this has a very interesting characteristic that I very much like. Unlike an SSD, DRAM has inherently very poor data durability and it is very easy and fast to erase anything. Unfortunately, since they are using a SSD controller, this might still not do what I expected it to do, but one of the big problems with SSDs is you cannot delete anything once written. You can secure erase all of the drive, but not just a few files, you only have the manufactuerer respecting TRIM.
The hope here is that because this controller uses DRAM, the contents of the drive can truly be erased quickly on command, while leaving other data intact.
One use case for this would be systems where file level encryption is untenable, but data can potentially be recorded that you would like to cryptographically remove. It would also provide plausible deniability for erasure of contents.