SSD drive as RAM?

Discussion in 'Mac Pro' started by Loa, Jul 4, 2011.

  1. Loa macrumors 65816

    Loa

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    #1
    Hello,

    Quick theoretical question for the gear heads!

    How much faster is DDR-3 RAM compared to top of the line SATA 3 SSDs?

    Could a modified interface (instead of SATA) help bridge that gap?

    Thanks!

    Loa
     
  2. Intell macrumors P6

    Intell

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    #2
    DDR3 is much faster than SATA3 speeds. The SSD would not only be slow, it would wear out rather quickly.
     
  3. simsaladimbamba

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    #3
    RAM works in GB/s. SSDs only work in MB/s. An SSD would be very, very slow RAM, but RAM would be a very fast SSD.
     
  4. CFoss macrumors 6502

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    #4
    Don't forget the fact that RAM is volatile (loss of memory when there's no power supplied to it). Kind of makes RAM impractical as a SSD.
     
  5. simsaladimbamba

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    #5
    Yeah, I forgot about the violent part.
     
  6. Intell macrumors P6

    Intell

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    #6
    Yea, those RAM chips can get pretty mean.
     
  7. Umbongo macrumors 601

    Umbongo

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    #7
    The latency is also nanoseconds vs. microseconds.
     
  8. MacinJosh macrumors 6502a

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    #8
    Back in the day I had an Atari STe with 4MB(!!!) Ram. It was maxed out. I used part of it as a ramdisk. It was freaking fast compared to a floppy. It would survive a soft-reset but not a cold-boot.

    Virtual memory is not a new concept. In the said Atari days there were utilites that would use HD space for ram. It was slow but it worked.

    Today all OSes use virtual memory. I guess it's called a swap file in OSX? Using a swap file on an SSD drive would no doubt speed things up.

    However, having to resort to using virtual memory means you need more physical memory.
     
  9. Vylen macrumors 65816

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    #9
    True, but RAM disks exist still.
     
  10. CFoss macrumors 6502

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    #10
    "Volatile memory, memory that lasts only while the power is on (and thus would be lost after a restart)"

    http://en.wikipedia.org/wiki/Volatile

    Under computer science.
     
  11. simsaladimbamba

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    #11
    Thanks, but I know what volatile means. I just thought of violent after reading that word.
     
  12. ActionableMango macrumors 604

    ActionableMango

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    #12
  13. Intell macrumors P6

    Intell

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    #13
    Volatile and violent are two very different things.
     
  14. MacBookPr0 macrumors regular

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    #14
    i bet that one day, once ssd's are much faster, theyll use them and well be able to run a computer like a super computer of today....

    just my thoughts
     
  15. theSeb macrumors 604

    theSeb

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    #15
    I actually laughed out loud. :D
     
  16. mac.tastic macrumors member

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    #16
    And pointless. I could understand if one side was RAM and the other SSD so that it would not just occupy a memory slot. But as a Pure SSD, there are far better places to hide a very small form factor. Such as making it with an adhesive or velcro backing so it could be put anywhere in the chassis.
     
  17. codymac macrumors 6502

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    #17
    They exist in the "enterprise" space.

    And that's about as much comment as I can give them publicly without getting the lawyers' approvals. Not kidding.
     
  18. mac.tastic macrumors member

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    #18
    Yeah, sure. If you had that kind of importance you wouldn't be allowed to post on public forums in the first place.
     
  19. alust2013 macrumors 601

    alust2013

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    #19
    What exist in enterprise?
     
  20. codymac, Jul 5, 2011
    Last edited: Jul 5, 2011

    codymac macrumors 6502

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    #20
    RAM based SSDs - although at this level it's more of a solid state storage solution than a "drive" solution.

    The opposite of what the OP asked, but the discussion kind of diverged a bit anyway.
     
  21. seek3r macrumors 6502

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    #21
    Depends on what you're using it for. For a project last year my team and I, on a cluster we built for a competition, used a 96GB ramdisk exported over Infiniband (IPoIB) to cluster nodes for *very* fast scratch and application space. We kept an async backup in order to have restore points.

    So yeah, ramdisks definitely have their place :)

    (for that matter, there are companies that make ram based SSDs that essentially hang ramdisks off the PCI-e bus and pair it with a battery backup to make sure data isnt lost prematurely)
     
  22. mac.tastic macrumors member

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    #22
    Lets not forget that Google's entire search database lives in ram.
     
  23. CountBrass macrumors regular

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    Mar 17, 2009
    #23
    Old hat: they're called ram drives.

    I think you've been had! (We use to disconnect the network cable from the new guy's PC and tell him we used AirNet in our office. It was much funnier before WiFi was even thought of. Perhaps you're the victim of a new-guy office prank).

    Also, Oracle can keep everything in memory (ie the entire database) if you want it to and either take the risk or put other mechanisms in place (multiple redundant servers split across physically separate data centres for example).
     
  24. Hellhammer Moderator

    Hellhammer

    Staff Member

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    #24
    Lets list down some numbers:

    Bandwidths

    DDR3 1066MHz (single-channel) - 8.525GB/s
    DDR3 1066MHz (dual-channel) - 17.1GB/s
    DDR3 1066MHz (triple-channel) - 25.6GB/s

    DDR3 1333MHz (single-channel) - 10.65GB/s
    DDR3 1333MHz (dual-channel) - 21.3GB/s
    DDR3 1333MHz (triple-channel) - 32GB/s

    SATA III - 0.75GB/s (or 0.6GB/s when considering the 8b/10b encoding)
    Fastest PCIe SSDs - ~4GB/s

    Latencies

    DDR3 1066MHz CL7 - 13.13ns
    DDR3 1333MHz CL9 - 13.5ns

    Intel 510 Series - 70 000ns
    OCZ Vertex 3 - 100 000ns
    OCZ Z-Drive R3 - 100 000ns

    I think the latency part tells you enough.
     
  25. Loa thread starter macrumors 65816

    Loa

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    #25
    Hello Hellhammer,

    As you implied, the connection type has a lot of impact on performance. What if we could use SSDs with the typical RAM connection?

    Also, the numbers you specified are theoretical. For example, for most apps, going from dual to triple channel memory has no effect whatsoever.

    And is the latency a matter of the memory itself, or the interface?

    Loa
     

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