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For Cat Fuzz Windows NT RAM & Pagefile Optimization

Discussion in 'Troubleshooting' started by SpiritWalker, Dec 14, 2001.

  1. SpiritWalker

    SpiritWalker Guest

    Windows NT RAM & Pagefile Optimization



    Unlike the MacOS (for example), NT was designed to use virtual memory without regard for the amount of RAM in your box. Even if you have a 768MB of RAM, NT still wants a pagefile, and NT will still use it. It’s for this reason that knowing how to optimize your overall system memory configuration is so important. It doesn’t matter if you’ve got 128 or even 256MB of RAM – if your pagefile isn’t in tip-top shape, you’re taking a performance hit, and that extra RAM you paid for isn't truly paying off. But how much RAM do you need in the first place? Well, it depends - there's no real simple formula, other than to say that if you have less than 128MB of RAM, you're suffering.

    I’ve seen it happen a hundred times. Some well-meaning user tries NT and loves it (who wouldn't, when coming from 9x?). Two weeks later this person will inevitably decide that their techie-bud "Frank" was probably right when he said that 128MB of RAM or more was the only way to go. Our protagonist heads out to buy the RAM, dreaming of the performance increase it's gonna provide. Upon returning home, s/he sticks in his box, boots 'er up and, yep, the system seems a bit more lively.

    That’s where most users leave off: only half way through the job.

    See, unlike Windows 9x, NT does not dynamically adjust the pagefile size. Even if you upgrade from 64 to 512MB of RAM, if you never adjust your original Virtual Memory settings, NT will page as if you only have 64, and you'll take a performance hit every time NT goes over your original setting (which will be often).

    Unfortunately, most users never question their virtual memory, or "pagefile", settings. That's too bad because there are numerous ways to improve upon the default settings NT will establish on install, many of which can really affect the speed of your machine. It's not uncommon to see someone who, upon experiencing a good amount of disk thrashing, heads out to buy more RAM when RAM isn't the problem. You have to be able to analyze your needs intelligently. You shouldn't even consider buying RAM without first taking into account the state of your pagefile settings.

    So, without further adieu, here's the Ars Guide to RAM and Pagefile mojo under Windows NT 4.0.

    First off, we're gonna assume that you've installed the latest service pack, and that you've enabled DMA for your IDE channels if they have devices that support it. (Chances are that your fancy new UDMA HD is not running in DMA mode unless you've forced NT to allow it to do so.) If our assumptions are wrong, we suggest you remedy that fact.



    How much do you really need?

    'Tis a question that has started many a fight amongst NT aficionados. Pretty much everyone agrees that 128MB of RAM is the true power user's minimum, but after that, the agreements stop. The good news is that there is a way to measure what you really need. The bad news is that, whatever you decide to go with, someone will always tell you that you're wrong. It doesn't matter: you can be pretty certain of what you need.

    What Microsoft says
    Microsoft wants you to have RAM + 12MB of Virtual Memory available for the system, regardless of how much RAM you have (some documents say RAM + 11, but most of those relate back to NT 3.1). The reasoning for this is because Microsoft designed NT to dump the system's memory to the pagefile in the event of a crash (a setting you can turn of). So, you need at least as much pagefile as you have RAM (at least so far as this reasoning goes). The additional 12MB is for overhead in said crash eventuality. So, if you have 128MB of RAM, MS would tell ya to set yourself up with 140MB of virtual memory.

    What we say
    In today's world, that recommendation doesn't really work. First of all, hard and fast rules don't tend to work in general - that's why we're all natural born tweakers, right? Secondly, the low price of RAM makes owning a 256+ MB RAM box a real possibility these days. You can't use the same performance rules for a 32MB box as for a 512MB box! So, we offer you three rules, and then a yardstick. First, the rules:

    For boxes with RAM less than or equal to 96MB, start with this: RAM x 1.75. So, on a 64MB RAM box, I'd recommend 112MB of pagefile space, giving you a total of 176MB of system memory. For boxes with 128+ RAM, go with RAM x 1.5. For boxes with 256MB or more RAM, go with the Microsoft formula of RAM + 12, unless you don't care about memory dumping, at which point I'd go conservative and try RAM x .75. But understand this: there's nothing wrong with your pagefile being too big, so if you're uncomfortable with the prospect undercutting Microsoft's recommendations, just go large.

    Now, these are just starting points. Rather than tell you what multiplier to use and leave you hanging, let's talk about how you can measure your needs from here.

    [Aside: I want to point out that those of you with a huge NT user database have another issue to take into account - the size of your SAM (the database that user account information is stored in). Your pagefile should be at least 2.5 times larger than your SAM. For most of us, that'd come to a few MBs. But for some people, that could be half a gig (and people who maintain those kinds of servers probably don't need me telling them this, anyhow :)!]

    OK, back to the real world. Let's talk about where to make it all happen, and how to measure your success.
     
  2. SpiritWalker

    SpiritWalker Guest

  3. OO7MIKE

    OO7MIKE Mr. Sexy

    Joined:
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    NICE..... to bad i cant use it :p
    win xp users might beable to get some use out of it.
     

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