[HN Gopher] Ddram disk - A PCIe card with 14x RAM slots
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Ddram disk - A PCIe card with 14x RAM slots
Author : cheuv
Score : 37 points
Date : 2022-05-30 12:20 UTC (10 hours ago)
(HTM) web link (ddramdisk.store)
(TXT) w3m dump (ddramdisk.store)
| liminalsunset wrote:
| An underrated use case for this would be for storage of sensitive
| information. Information stored on a non volatile device is
| difficult to erase (Format NVM/ATA Secure require power cycle,
| hard drives require time to actually wile). Even if the data is
| encrypted, it is vulnerable to xkcd's "rubber hose decryption".
|
| With DRAM, the storage media itself is fairly volatile and power
| removal/memory content initialization should be much faster.
| halJordan wrote:
| Apple solved this problem at scale some time ago. Im not sure
| slamming ram on a pcie card is a better solution than including
| a piece of effaceable storage somewhere.
| resonator wrote:
| There is a lot more technical information at
| http://ddramdisk.store/.
|
| It's slower than RAM, runs at around full pcie 4x speed of 7GB/s
| but it upports way more capacity than most boards would allow.
| humanistbot wrote:
| What is the competitive advantage of this versus NVMe? Their 1TB
| ramdisk is $1000, while a Gen 4 NVMe PCI-e card gives the same
| speeds in a smaller and more standard format for $150-$200.
| theandrewbailey wrote:
| RAM doesn't have a fixed number of write cycles. It can be
| written to indefinitely, but NVME flash has an estimated number
| of TBs that it can write before it fails.
|
| RAM is volatile (the data is destroyed when the power is cut),
| which can be a security feature. There appears to be a battery
| backup on these boards, but I imagine that it can be removed
| easily.
| steeve wrote:
| Latency maybe?
| Nexxxeh wrote:
| Write endurance I guess would be one.
|
| Samsung 980 Pro is under warranty up to 600 TBW.
|
| I don't know if that is external data written, or also includes
| whatever overhead the drive's internal processes have, which I
| imagine is higher when you run it near max capacity.
|
| RAM has virtually unlimited write endurance.
|
| I was interested for CCTV recording, as it can be murder on
| standard HDDs and consumer SSDs. Continuous writing at whatever
| the total bitrate of all cameras is, plus whatever index you're
| using, plus whatever clips its generating.
|
| Ideally HDD for the constant, SSD for the clips and index.
|
| I had a small (120GB) clip and index SSD drive start to
| struggle in a dirt-cheap non-critical system and found it had
| written 42TB in a year. Now part of that was poor
| configuration, but the drive was REALLY starting to struggle,
| throughput would occasionally drop off a cliff.
|
| The system was battery backed, so a RAM disk would have been
| fine, and on triggering the UPS I'd have it just copy the
| contents to a fast HDD.
| [deleted]
| jmalicki wrote:
| Speaking as someone who actually runs NVMe RAIDs for large-ish
| databases, the NVMe speeds quoted are usually only attainable
| for large sequential streaming loads. While they are not
| spinning disks with heads that need to seek, there is still
| very substantial random I/O overhead with SSDs, including NVMe.
| Even with a top of the line model like a Samsung 980 Pro, you
| might only get 5% the PCIe 4 bus speed with heavy random IO
| performance.
|
| RAM has cachelines and such, but postgres reading 8k at a time
| isn't limited by that.
|
| How to work something like this into Linux as say, a very fast
| swap device, is another question.
| xbmcuser wrote:
| With ddr5 entering mainstream we will soon have a lot of used
| ddr3 and ddr4 modules available for cheap.
| anfractuosity wrote:
| Out of interest, would you get a similar bandwidth using DDRx on
| this card over PCIe, to using DDRx in the standard memory sockets
| on a motherboard
|
| Edit: Looks like the slowest DDR4 gives 19200 MB/s
| https://uk.crucial.com/support/memory-speeds-compatability
|
| Not sure what PCIe that card supports is though
| convolvatron wrote:
| I haven't kept up with the speed and feeds, but in general PCI
| bandwidth is a decimal order of magnitude less than all the
| memory controller bandwidth
| theandrewbailey wrote:
| Looks like the card is PCIe 4.0 x4, which gives about 8GB/s.
| Not sure if this board is driving the RAM at full speed, or how
| many controllers there are, but more lanes could make this
| faster.
| LinuxBender wrote:
| It seems these are not produced any more? [1] If someone is
| currently manufacturing a battery/capacitor backed memory card
| that accepts several DIMM's of the recent memory modules _like
| 32GB+ ea._ I would be interested. There should be benchmarks from
| a popular 3rd party reviewer.
|
| [1] - https://superuser.com/questions/1508905/is-there-a-modern-
| ra...
| aeaa3 wrote:
| Is this for real? The store, which looks pretty amateurish, has
| no products for sale ("out of stock") and the prices are vastly
| too good to be true.
|
| DDR3 memory for 40c per gigabyte? Cheapest I can see on Amazon is
| 5 times that. 256GB of memory (plus the board itself) for $280?
| Not possible.
|
| Sorry, I don't believe it.
| wtallis wrote:
| I'm also doubtful that a memory controller with the necessary
| pin count can even fit under that heatsink. 14 DIMM slots can't
| all be sharing just one or two 64-bit channels at anything
| approaching standard speeds and timings.
| farkanoid wrote:
| Something seems a bit dodgy. The about page shows the top and
| bottom PCB layouts without any RAM sockets, only dozens of DDR
| RAM ICs soldered directly to the back of the card.
|
| ...Which would be fine, had I not stumbled upon (what seems to
| be) the original project[1], in Russian no less.
|
| The blog shares the same block diagram, images and DDR PCB
| layout. There are no DDR RAM slots. Further, the slots are
| through-hole and not SMD, you wouldn't be able to attach a
| heatsink directly to the back of the card as shown in the
| images.
|
| [1] https://habr.com/ru/post/567742/
| rincebrain wrote:
| That doesn't seem to be the original, given that Google
| Translate translates the top of the article as "originally
| posted by" with a link to ddramdisk.tech, which 404s now, but
| originally [1] did not.
|
| [1] - https://web.archive.org/web/20210714152011/https://ddra
| mdisk...
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(page generated 2022-05-30 23:02 UTC)