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A few years ago I heard something about the maximum recommended usage for an NTFS volume not exceeding 50% otherwise it's performance would drop drastically. I do not recall any arguments just the statement.

I've tried to search for any support of this theory on the web but didn't find anything. Could anyone please advise me on that?

Basically I'm deciding on how to split an disk drive knowing my system volume is slightly over 50GB used. Should I double it and make it say 110 GB or is it just a waste of space?

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If I had to recommend a formula, I'd say 4E8 * (log10(capacity) - 9). – Mehrdad Mar 6 '12 at 7:07
Is this a joke? – User Mar 6 '12 at 7:18
Not really, I'm quite serious... are the results unreasonable? – Mehrdad Mar 6 '12 at 7:24
I assume this formula gives back the recommended usage value from the volume capacity. If I feed it 100 (GB) it gives us -458752. WTF? – User Mar 6 '12 at 7:29
You need to feed it 100E9, not 100. – Mehrdad Mar 6 '12 at 7:37

NTFS does its best at any given size, but to answer your specific question, NTFS's performance does tend to fall off after about 85% capacity because the natural fragmentation of the disk suddenly starts to get in the way of allocating new sectors for file data - with larger fills such as 95% taking markedly longer to perform simple operations such as file moves, renames and deletes.

If you do need to keep NTFS at a fill much above this (and the content is not largely static) your best bet is probably to run a scheduled defrag on the disks every night to try and reclaim as much fragmented memory as possible for the next day's work.

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Windows 7 automatically defragments the C drive on a schedule by default. – Moab Mar 7 '12 at 4:41
True, but it only does so weekly. If your NTFS volume is at 95% capacity that won't be often enough. – SecurityMatt Mar 7 '12 at 12:58

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