back to article Windows Server 2016 persistent memory support supercharges storage IO

Analysis The best IO is... no IO. Windows Server 2016 has code to supercharge data storage IO speed by not treating it as IO anymore. It uses storage-class memory (SCM) as a persistent store, one that is on the memory bus, close to the CPU, and doesn't lose its contents when power is lost, an NVDIMM-N type device. That can be …

  1. Lee D

    Only a stopgap until everything is NVRAM, and then all this half-way technology will become obsolete.

    I can't think of a single reason that NVRAM can't replace all current RAM and SSD storage in time, or why you would not want it to?

    So long as you have a button that allows a "memory clear and boot" if you ever really need it, I think it's a no-brainer.

    Like USB flash drives being used as "fast cache" for the storage devices of old, or hybrid SSD drives, it seems like one of those technologies that will only obsolete itself if it gets popular.

    1. defiler

      "Can't think of a single reason"

      I can. Virtual server mobility. It's much easier with a SAN to hold the drives.

      Don't get me wrong. For properly big jobs you'll want to run it on bare metal and cluster (even if it ends up being something like log shopping or AlwaysOn Availability groups), and at that point you don't need the mobility. If a node fails then another picks up the load.

      For small/medium shops, though, this is overkill and inconvenient. Like every finely tuned tool, good for a specific job and useless elsewhere...

    2. Cameron Colley

      "memory clear and boot"

      Aha, but wouldn't that clear everything including the OS?

      I gave myself the thought-experiment of "How does an OS purely stored in [persistent] RAM* work?". Binaries aren't "loaded form disk into memory" they're just, what, jumped to?

      *That is, when storage and memory become the same physical thing.

      1. Ian Ringrose

        Maybe just like a AS400

        As I understand on the AS400 apps are loaded into the virtual address space when they are installed, not when they are started.

      2. Richard 12 Silver badge

        Re: "memory clear and boot"

        Yes. It is conceptually very easy to do in fact.

        Right now the UEFI (or das uboot etc) bootloader loads GRUB or the Windows loader from persistent storage into RAM, which then copy (and maybe decompress) the next loader or kernel image from persistent storage into RAM.

        That first bootloader could just as easily jump straight to a kernel image say in NVRAM.

        This is how the majority of microcontroller bootloaders have always worked.

        The scary bit is that a power cycle won't clear the NVRAM back to a known state, it requires running software to do that. Viruses are therefore far more dangerous as you cannot "clean boot" the system anymore.

    3. Naselus

      That's pretty much where we're headed, yes. In storage terms, it's actually probably more economical to only build up NVRAM fab capacity, too, since fresh SSD capacity is almost certainly not going to be about to recoup it's gigantic outlay prior to obsolescence now. The same will probably be true of RAM fairly soon too, and eventually HDD too.

      In terms of it replacing actual RAM... well, unless you want to rethink the whole PC architecture to jettison the present role of RAM, we'll probably keep an at least nominal split between the two, for legacy reasons if nothing else. And as posters above note, not being able to clear the RAM without wiping your whole drive is a major downside which makes having the two split quite useful.

  2. Mage

    storage-class memory (SCM) as a persistent store

    Hardly rocket science and on some PDAs 30 years ago. Presumably easily added to almost any OS via driver, kernel module or whatever.

    It's more a case to of economics than software. I seem to remember servers with battery backed RAM too, apart from battery backed SRAM then DRAM on RAID controllers, so uncommitted cache wouldn't be lost by sudden power cut (or something)?

  3. Hurn

    Cherry Picked Opponent?

    Is it me, or does the 55-58 MB/sec transfer speed to NVMe SSD seem a little slow?

    1. Anonymous Coward
      Anonymous Coward

      Re: Cherry Picked Opponent?

      Single threaded, queue depth 1, so latency test, sustained write. Nvme drives are fast, with large queue depths for short periods, using the ram cache on them for taking the bursts.

      1. Richard 12 Silver badge

        Re: Cherry Picked Opponent?

        They're trying to compare the speed of "physically on the nonvolatile storage media", rather than the efficacy of the various caching schemes for the particular dummy workload in the test.

        After all, writing to disk normally returns much faster than the disk can actually write as it gets cached by the OS in RAM, then spooled out to the actual disk hardware, which caches again and finally writes to the physical media.

  4. Rainer

    Reminds me of...

    ...the STEC ZeusRAM, an 8 GB capacitor-backed RAM-disk.


    Those new NVDIMMs would probably also be great as ZFS log-devices ;-)

    1. batfastad

      Re: Reminds me of...

      Or the Gigabyte i-RAM from 2006...

      I remember we got one of those for a particularly busy (and poorly optimised) database and it was just the coolest thing. I remember thinking "this will be the future - no moving parts".

      1. Mikey

        Re: Reminds me of...

        Man, I remember the i-RAM... Always wanted to get one, then saw how much it cost... unpopulated. I'd love a more up-to-date version that could hold a more meaningful amount of DRAM now, as battery tech and the cost of the DIMMs are much better than way back then. Mind you, you're only one extended power failure away from losing everything on it...

        I do recall a similar drive that used a CF card and capacitors to back up the DRAM in the even of a power failure...

        (One quick Google search later)

        Aha! it was the ACARD ANS9010... And apparently they still make it. I may even see about getting one...

        Edit: Never mind, still the same old one, and only uses DDR2... bleah. So much for that.

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