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SSD 80% capacity efficiency

I forget where I read it, but I read that running an SSD at 80% of max capacity is best for optimal performance. Then recently I heard someone else say 70% is best. Which is it? Is it 70/80% of the actual reported amount of space or the amount listed on the box?

I was considering a 120gb ssd and a cache ssd but that is gone down the toilet. Now I am wondering if I should just get a 240gb SSD or 2 120gbs. 2 120s would be cheaper than a 240gb (Which is kinda of stupid). What concerns me is if I buy a single 240gb I would only be able to use 168/192gb of the space. Would I be able to use a higher % on a higher capacity drive?(Yes I am aware that two 120gb drives would yield me the same amount of space.) 80% hurts but not as much as 70%.
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More about capacity efficiency
  1. here is a link to the ssd optimization guides:

    http://thessdreview.com/category/ssd-guides/optimization-guides/
  2. Best answer
    Unlike HDDs, modern SSDs shouldn't slow down when they fill up. Whoever told you that 70% nonsense is talking out of his ass. SSDs have spare area reserved out of the box, anywhere from 7-20% I believe, so look at the useable capacity in specs and that's what you're getting. You don't need to lower the capacity any further
  3. 70% is a little high or the other way to look is leaving 30% free for OP (Over-Provision). A SSD is similar to hard drive as more full the drive gets, the write speeds can slow down (has no effect on read). This steams from OP/GC/TRIM needing free space to work with. Here is a thread on the OCZ forum, which goes into more details... http://www.ocztechnologyforum.com/forum/showthread.php?85029-Understanding-SF1200-drives-TRIM-OP-area-use-and-Life-write-throttle

    I recommend keeping roughly 10 to 15% free and limit (or avoid) running benchmarks, as they quickly eat up your OP and can cause the drive to throttle (more seen on Sandforce SSS's).
  4. Here's a link to the results of a 3 month long performance experiment:

    http://www.legitreviews.com/article/1618/1/
  5. Best answer selected by eric4277.
  6. If only I could give more than one best answer. thanks
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