Windows 7 Allocation Unit Size

Question

hello!

I don't know if it's the right place to ask such a question but I wanted to know which Allocation Unit Size to use for formatting a hard drive of 320GB under Windows 7

I have 8 options from 512 bytes to 64 Kilobytes. By default it's set to 4096 bytes.

so should I increase or decrease it to get optimal performance? no problem for the storage if the total storage available will decrease, it's not used anyway.

Thanks.