i-RAM as a Paging Drive

One question that we've seen a lot is whether or not the i-RAM can be used to store your pagefile. Since the i-RAM behaves just like a regular hard drive, Windows has no problem using it to store your pagefile, so the "can you" part of that question is easily answered. The real question happens to be, "should you?"

We have heard arguments on both sides of the fence; some say that Windows inefficiently handles memory and inevitably pages to disk even when you have memory to spare, while others say that you'd be stupid to put your pagefile on an i-RAM rather than just add more memory to your system. So, which is it?

Unfortunately, this is the type of thing that's difficult to benchmark, but it is the type of thing that's pretty easy to explain if you just sit down and use the product. We set up a machine, very similar to how we would a personal system, but tended to focus on memory hogs - web pages with lots of Flash, Photoshop, etc. Of course, we opened them all up at once, switched between the applications, used them independently, simultaneously, basically whatever we could do to stress the system as it normally would be stressed.

At the same time, we monitored a number of things going on - mainly the size of the pagefile, the amount of system memory used, the frequency of disk accesses, pagefile usage per process... basically everything we could get our hands on through perfmon to give us an idea if Windows was swapping to disk or not.

The end result? There was no real tangible performance difference between putting more memory in the system and using the hard disk for the pagefile or putting less memory in the system and using the i-RAM for the pagefile. Granted, if we had a way of measuring the overall performance, it would have shown that we would be much better off with more memory in the system (it runs faster, and it is accessed much quicker than off the i-RAM).

The only benefit that we found to using the i-RAM to store our pagefile was if you happened to have a couple GBs of older DDR200 memory lying around; that memory would be useless as your main system memory in a modern machine, but it'd make a lot better of a pagefile than a mechanical hard disk.

One more situation we encountered that would benefit from storing your pagefile on the i-RAM was those seemingly random times when Windows swaps to disk for no reason. But for the most part, our system was slower when we had less memory and stored the swapfile in it than when we had more memory and less swap file.

Adobe Photoshop is a slightly different creature as it keeps a scratch disk that is separate from the Windows pagefile. We tested Photoshop and used the i-RAM as our scratch disk, but in all cases it always made more sense to just throw more memory at Photoshop to improve performance where we ran out of memory. If the operations you're performing in Photoshop can fit into system memory, then you'll never touch the scratch disk.

Overall, based on our testing, the i-RAM doesn't make much sense as a paging drive unless you have the spare memory. The problem with "spare" DDR200 memory is that it is most likely in small 64MB, 128MB or maybe 256MB sizes, which doesn't buy you much space on an i-RAM drive. For most people, you're much better off just tossing more memory in your system.

i-RAM Pure I/O Performance i-RAM as a boot drive
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  • NStriker - Thursday, July 28, 2005 - link

    Anand quotes $90 per GB of RAM here, but I'm wondering if the I-Ram works with the much cheaper high-density junk you see out there all the time. Like 128Mx4 modules. On motherboards, usually only SiS chipsets can handle that type of RAM, but there's no reason the Xilinx FPGA couldn't.

    Right now I'm seeing 1GB of that stuff for $63.
    Reply
  • jonsin - Thursday, July 28, 2005 - link

    Since Athlon64 north bridge no need the memory controller. Why shouldn't the original memory controller used for iRam purpose. By supporting both SDRam and DDR Ram, people can make use of their old RAM (which no longer useful nowadays) and make it as Physical Ram Drive.

    Spare some space for additional DDR module slot on motherboard exclusively for iRam, and additional daughter card can be added for even more Slots.

    Would it be a cheaper solution for iRam ultimately ?
    Reply
  • jonsin - Thursday, July 28, 2005 - link

    And more, power can be directly drive from ATA power in motherboard. By implementing similar approach to iRam, an extra battery can power the ram for certain hours.

    By enabling north bridge to be DDR/SDRam capability is not a new technology, every chipset compnay have such tech. They can just stick the original memory controller with lower performance (DDR200, so more moudle can be supported and lower cost) to north bridge, the cost overhead is relatively small.

    What I think the extra cost comes from extra motherboard layout, north bridge die size, chipset packaging cost (more pins). I suppose it can cost as low as $20 ?
    Reply
  • jonsin - Thursday, July 28, 2005 - link

    More, the original SATA physical link can be omitted as the controller in North Bridge can communicate directory to SATA controller internally (South bridge thru HT ?) In this case, would the performance increate considerably and the overall layout more tidy ? (no need external cable and cards) Reply
  • mindless1 - Friday, July 29, 2005 - link

    NO these are all problems. The purpose is to have a universal platform support that is gentle on power consumption. That means a tailored controller and even then we're seeing the main limit is the battery. "Tidy" is an unimportant human desire, particularly less important inside a closed PC case. All they have to do is route bus traces well on the card and be done. Reply
  • slumbuk - Wednesday, July 27, 2005 - link

    HP sell an add on for their DL 380 server for $200 (at discount) that gets you 128MB of disk write cache... makes a good system also fast for disk writes.

    This card could be used by linux vendors to enable file-system data and control logging for similar money for GB(s) of write cache... Cheap, reliable, fast general purpose file servers.. that have fast disk write speed without risking data loss.. Speed meaning no disk-head latency, no rotational latency - just transfer time.

    It would sell better with ECC memory.. or the ability to use two cards in a mirror.. at least to careful server buyers..

    Reply
  • slumbuk - Wednesday, July 27, 2005 - link

    You could set up the iRam drive as the journal device for Resier or Ext-3 logged file systems - and log both control info and data - for fast, safe systems without too much fuss.

    I think I want one - but not as much as I want other stuff..
    Reply
  • AtaStrumf - Wednesday, July 27, 2005 - link

    Interesting but hardly useful for most. Kind of makes sense to only make 1000, but of course that's where the $150 price tag comes from. Reply
  • rbabiak - Wednesday, July 27, 2005 - link

    i guess it would add to the base board cost, but a SATA controller on the PCI card would make it a littl nicer as then you are not takeing up one of your SATA channels, i only have 2 and they are current both used for a Raid-0

    Also if they made the PCI card a SATA interface and then short circeted the backend to conect directly to the memory, wouldn't they then be able to get much higher transfer speeds than sata and yet all the existint SATA divers could be used with it, given they emulate a existing SATA interface.
    Reply
  • DerekWilson - Thursday, July 28, 2005 - link

    Better to use the onboard ports ...

    a 33MHz/32bit PCI slot only grants a max of 133MB/sec. This would make the PCI bus a limiting factor to the SATA controller.

    Step beyond that and remember that the PCI bus is shared among all your PCI cards. Depending on the motherboard some onboard devices can be built onto the PCI bus.

    With bandwidth on current southbridge chips already being dedicated to SATA (or SATA-II), it would be a waste in more ways than one to build a SATA controller into the i-RAM.

    That's my take on it anyway.

    Derek Wilson
    Reply

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