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I am new to the hardware side of things. I run a few machines which have 400GB+ SSD's and 32GB RAM. I have been thinking about going up to 64GB RAM, however, I was thinking, since SSD's are solid-state like RAM, can't my extra space be used as RAM?

If I do this, will the extra RAM (from disk space) be significantly less efficient than DDR3 RAM?

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Isn't that basically what "swap"/"pagefile" functions in modern OSes are doing? –  grawity Jul 10 '13 at 9:44
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Because SSD have limited writes, and your system makes hundreds of writes to your memory every hour, which means a SSD device would have a lifespan of a few days at that rate. Plus in terms of pure speed SSD is extremely slow compared to memory. Random Access Memory does not store the values after the power has been turned off, NAND the memory sed in SSD hardware does. NAND would make horrible Random Access Memory for a lot of reasons other then speed. –  Ramhound Jul 10 '13 at 10:53
    
If it were that simple, wouldnt everyone be doing it? –  Keltari Aug 4 at 16:47

4 Answers 4

Firstly, RAM is still significantly faster than both your regular 6gb/s SATA or even the newer PCI-e based solutions. RAM is also designed to be written and erased repeatedly, at the cost of volatility. RAM generally dosen't wear out due to use regular use - tho, of course, it can fail like any component.

While the lifespans of SSDs have gotten much better, SSDs do wear out. They're absolutely brilliant for non volatile use, but if you wrote and overwrote NAND (which SSDs contain) like you do RAM, it would wear out.

Both are really optimised for different things, and you're better off having enough RAM (and using SSDs or spinny hard drives for paging out) than compromising on enough RAM for the task.

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As grawity suggested you already have the swap/page file performing this task. Now even an SSD is much more slower compared to DDR3. SSDs can deliver up to about 654MB/s while 1333MHz DDR3 in dual-channel mode can deliver up to 21.3GB/s (21 332MB/s).

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Yes, it will be significantly less efficient than DDR3 RAM.

  1. SSD will wear off quickly if used as RAM (frequent writes). So it will only be effective for 2 months or so, after that it will surely die. (So instead of 10 years of life ... it will live for about 10 weeks.)
  2. SSD is a disk device. CPUs can ONLY pre-LOAD data into its cache from RAM. If it will be on an SSD, it must be first LOADED into RAM... Accessing the disk (even very-fast SSD) is around 100 times slower than accessing RAM. See benchmarks of HDD, SSD and RAMDISK (ramdisks on DDR3 have more than 3000 MB / sec , and less than 0.1 milisecond wait time for access. So, clearly: SSD cannot compete with speed of RAM).
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What I have done for a webserver is creating a virtual drive in memory with imdisk. This drive is used as temporarily space (sessions, log, cache and temp files) to reduce write and read delays on each request. The websites are placed upon a SSD. This is working pretty well and fast.

The next thing I want to do is create a virtual drive at boot that makes a copy of the websites on SDD to memory. You can also use a HDD as source ofcourse. I can think of three benefits.

  1. Blazing fast seek times and read speed
  2. When server is attacked and files of website are changed, simply reboot and problem solved. The original files are kept in a safe place somewhere on the SSD.
  3. Life-span enhancing of the SSD drive.

The problem I have is that I need more memory, for example 16GB. I don't have it right now but you have it! You can try this.

One thing you need to know is that you need a script to do all this things for you. Create the disc at boot, copy the files and start the server.

Give it a try!

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