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I've heard numerous times in the web hosting industry that using "too much" disk space on a drive is bad for performance. Is this just a myth? Can someone explain why this is an issue, even in a situation where the amount of IO done to the drive would be the same at 10% as it would be at 90%?

I'm especially curious in the case of virtual servers. If I set up 10 Logical volumes as the virtual disks for some VMs, is it going to run better if I "waste" 20% of the disk space?

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The less free space there is on a drive, the more fragmented newly-created files will be. Imagine two hotels, one mostly empty, one mostly full. Three people want rooms next to each other. Which hotel will be more likely to be able to give it to them?

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I can appreciate the fragmentation argument, but wouldn't that be a much more linear problem than what a lot of people suggest using a high amount of disk capacity causes? I've heard numerous times from people that once you approach 90% things slow down drastically. If fragmentation was the only issue here, wouldn't the difference between 10% and 30% be more pronounced than 85% to 95% in regards to performance? –  GoldenNewby Nov 26 '12 at 22:56
    
Ohhhh.... I see what you are saying. So this would not be the case for VM's then. Got it. –  GoldenNewby Nov 26 '12 at 23:00
    
@GoldenNewby: No. With 10% full or 30% full, there's tons of free space and you'll almost never be forced to fragment it. With 95% full, you have very little free space so it will be extremely hard to find contiguous chunks. (A movie theater is a good analogy. A party of 4 can almost always sit together in a movie theater that's less than 60% full. But if it's 95% full, forget it.) –  David Schwartz Nov 26 '12 at 23:38
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