Riding on the memory bus: Micron brings out 8GB flash DIMM Micron is launching an 8GB flash DIMM, providing competition for SanDisk and its ULLtraDIMM. Flash DIMMs mount a flash chip card on a DIMM socket, putting the NAND on the memory bus, which is even faster than the PCIe bus. The idea is to provide an intermediate store or cache between main memory and PCIe flash or SAS-connected …
... these would be ideal for seperate data and code storage, interpreted code in flash with dram as a workspace and data store.
Sadly without the above model access times make data in flash typically a bad investment, unless they add fast hardware decompression then processing stalls are going to increase reducing any benefit from not having to swap memory out
HOW DOES THIS WORK DAMMIT?
If they fit in a RAM slot then presumably they look just like regular RAM to the OS.
There are a few ways it could be used:
* reserve it the same way as you would a block of physical memory and have something like /proc/kcore so that userland processes can mmap parts of it (use it like regular memory)
* make it look like a block device that you can put partitions on and mount and so on (treat it like a disk drive)
* keep it all for the kernel and use it transparently in some subsystems like software raid, filesystem journal, disk cache, etc.)
>HOW DOES THIS WORK DAMMIT?
As I understand it.... They go in normal slots, they operate at DRAM speed, if the power goes they back-up to flash that is also on the DIMM.
I guess you effectively get a machine you can just pull the plug on then when you turn it back on it's on instantly (although if it takes 40secs to back-up the RAM then it'll take 20secs to boot).
Unless you are using a full server MoBo then I don't see the use for this.
Yeah, but I _am_ using a full server MoBo (several of them) to provide some bigass storage boxes, and if I could fill their spare ram slots with this stuff for cache + intent log purposes that would improve the throughput I get really dramatically. This is a brilliant, brilliant idea for enterprise storage.
...if it works. Like everyone else I can't seem to get any detailed information on how this would fly in practice.
This is why I am interested. The performance boost sounds great, but given the complexities of server RAM, and the propensity to require matched DIMM pairs/triplets in order to even boot, I dont understand how it would work.
One assumes a memory controller firmware upgrade would be required at a minimum? (that'll be a new CPU then).
My thoughts were along similar but different lines: 8GB?
You can get an 8GB DRAM DIMM for little cost. OK, it's not persistent, but it's faster.
When I envisioned Flash DIMMs, I was expecting much larger capacities than currently available as DRAM.
There will be use cases, but I can't see them unless the cost is significantly lower than DRAM. Even on a server motherboard, the number of DIMM slots is often a restriction. A 32/64GB Flash DIMM, however...
Looks like the Micron DIMM is a NVDIMM-N providing Flash backup of the DRAM contents during pfail.. Diablo products are NVDIMM-F where the Flash storage is used during normal system operation. They are quite different beasties despite both using flash.
- so far inside this my head hurts, but not authorized to speak, so just a small bit of information -
NV memory is marching ever closer to the CPU. This particular model is only a baby step in that direction and not necessarily a useful one, but it's obvious that NV memory and CPUs are cozying up to one another. Whether it's this model or some other high BW low latency connection scheme, it's going to be interesting. Intel/Micron and others are determined to breach the memory wall.
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