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While studying for the A+ Exam I was reading about SSD's and I thought to myself that if you had a mobo with a low RAM limit you could use a dedicated SSD purely for Virtual RAM. I looked up some info on line and the info I found said that this was a poor practice but didn't explain why. Why shouldn't SSD's be used for Virtual Memory and what are your thoughts on a dedicated Virtual Memory drive? Thank you!

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If you can afford a SSD, I doubt your motherboard has a low RAM limit. RAM is cheaper and faster then a solid-state drive, and SSDs should NEVER be used for virtual memory!!! They have a limited number of writes, and using them for virtual memory often will severely reduce the lifespan of the drive. (Yes, I agree that they're faster then using a HDD for virtual memory, but if you're paging out even to a SSD, you're still paging out 10-20 times slower then RAM...). –  Breakthrough Nov 16 '11 at 12:58
    
I believe he's using "virtual memory" in this context to mean "RAM drive". –  Bigbio2002 Nov 17 '11 at 16:53
    
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While people are suggesting you do not put a page file on SSD there is nothing to stop you, there are also similar-ish ideas such as Microsoft's Readyboost, though it uses a USB stick instead of an SSD. It works in a vaguely similar fashion (caching hard disk reads instead of caching virtual memory - but the theory of the method of performance boost and flaws are the same) but has very similar reasons for limitations as putting a page file on an SSD:

  1. Flash based memory has much poorer write tolerance than spinning-platter or full-on memory chips. Typical flash devices these days are getting as low as 5,000 write cycles for a standard MLC device, with the manufacturers using wear-levelling algorithms to help the device last longer. Sadly it seems that many SSDs fail after 1-2 years (see here for some failure rates during the first year), but this is typically due to failure of the SSD's hardware or firmware, rather than wear of the flash memory.

  2. USB sticks are dirt cheap, come in all the major helpful sizes (4GB, 8GB, 16GB and so on) and for small reads and writes are pretty comparable to an SSD. They suck at bulk transfers though.

There is also Intel's latest Smart Response which is effectively another version of the ReadyBoost technology.

So as long as you don't mind the idea that you could potentially wear the SSD out faster (though no faster than putting the entire OS on the SSD to be honest) then there is no reason not to put your page file on the SSD as it should perform better than the hard disk.

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What he's suggesting is not like Readyboost at all. Readyboost uses flash as a disk cache, to accelerate disk I/O under normal conditions. He's talking about using flash as a paging file, to accelerate paging (which only matters under abnormal conditions when the system is paging). At least, that's how I understand his term "virtual RAM". –  David Schwartz Nov 14 '11 at 19:20
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While Readyboost is not exactly what was being asked for it achieves very similar ends by using a flash device to service reads and writes that would otherwise go to a slower device. It is the closest we have to SSD as a pagefile device and my other points about why-not-to-do-it are still valid. –  Mokubai Nov 14 '11 at 19:30
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How is it the closest we have to using SSD as a pagefile device when you can actually use SSD as a pagefile device (simply by placing a pagefile on a filesystem on the SSD)? –  David Schwartz Nov 14 '11 at 21:12
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@techie007 Yep, our very own Jeff Attwood: The Hot/Crazy Solid State Drive Scale –  Mokubai Nov 14 '11 at 22:08
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@Mokubai I completely, 100% disagree with your entire answer. What ReadyBoost does is nothing whatsoever like putting a page file on a flash device, the theory of the method of performance boost is completely different (one uses the flash as a disk cache to accelerate random reads under normal conditions, the other uses flash as a page file to reduce the performance penalty of low-memory conditions). There is no reason to expect one to be anything at all like the other. –  David Schwartz Nov 28 '11 at 5:30
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SSDs are slower than RAM, but faster than HDDs. So, the obvious place for an SSD to fit into virtual memory is as swap space (swap partion in Linux; page file in Windows). The operating system automatically uses the swap space as needed when RAM is in short supply, so by putting swap on the SSD, you get faster-than-HDD performance when swap is needed.

On Windows the page file normally lives at C:\pagefile.sys, so to put that on SSD you'd have to either put your C: drive on SSD, or somehow tell Windows to put the page file elsewhere.

The other method that you seem to be suggesting is to somehow make the SSD look like additional RAM to the OS. I don't know how you would do that, but I agree that it would be a bad idea, since SSDs (flash memory) are slower than RAM.

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This is what it boils down to. While SSDs are fast compared to traditional HDs, RAM is significantly faster. While SSDs latencies are measured in milliseconds, DRAM has latencies in nanoseconds, and systems have bandwidth measured in several GB/sec, compared to several hundred MB/sec for SATA. –  afrazier Nov 14 '11 at 20:02
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I am using a 60GB SSD as a dedicated virtual memory drive running on windows 7 it is SATA-3 and I'm getting speeds of 450MB sec.

My machine is fully loaded with 32GB memory in all available slots. I'm using this machine to edit feature length movies in HD so this memory is quickly eaten up.

I have to say that the SSD virtual memory drive is a great help in reducing the bottleneck when memory runs low and VM kicks in. I don't care if the drive dies in a year or two, I'll just replace it with another cheap drive.

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Since RAM is currently cheap and SSD's are horrendously expensive, it doesn't make sense. You can buy 12G of RAM for something like $80. That would be the same dollar amount as a SSD and granted the SSD is larger, but, it eats an SATA port, adds heat, takes more power than RAM. If you have enough RAM, you normally won't be swapping so much to the virtual memory. Most of the SSD wouldn't be used anyway. Only about 3Gig would normally be used. For 4Gig of RAM, the price would be even cheaper.

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That's great, as long as you're using a 64 bit OS. Anyone with a 32 bit OS or a system that's limited in RAM capacity, this "SSD as swap" idea could be a very significant solution for them. –  Syclone0044 Nov 14 '11 at 20:45
    
@Syclone0044 there is no RAM limit on any n-bit operating system so long as memory support is added properly. Windows 32-bit variants have been capable of addressing more than 4GB of memory for many years now. –  Breakthrough Nov 16 '11 at 12:39
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