How do i keep alittle free space on my disks??

[whitewraith]

I am using unraid as a media server. I would like to leave about 500GB free on each disk in the array.  I have read posts and posts and posts about minimum free space but no clear instruction on how to do it. I thought it was tied to the Minimum free space for the share, but that it not so.  I have it set at 500GB and it fills disks past that. I am also wondering when unraid switches to another disk, does it wait for a error to come that the file cant be written to disk due to lack of space? I am using Krusader to transfer large amounts data to my share. If it cant write a file will unraid tell it to try again using a different disk? Or do I have to only move the amount of files to fill up the drive but not go over.