Bad idea to fill up 100% of data drive capacity?

[paperclip]

Let's say I have five 2TB data drives. Is it best to successively fill them up to 100%, or should I tell Unraid to leave some space unused by setting a "high water" amount? If so, how much unused space should remain per disk? This is a performance-related question.

[Rajahal]

It is best to leave a bit of free space on each.  How much space depends on what you store on the drives.  The easy rule of thumb is to leave at least the amount of space needed to make a copy of your largest file.  So if your largest file is a 4.5 GB DVD ISO, then leave about 5 GBs of free space.  Something about 'replaying journaled entries'...I don't really understand it, but the other hero members can explain.

[prostuff1]

I usually leave around 10-15 GB free on a drive.  That usually amounts to 2 full .iso rips of a DVD

[WeeboTech]

General rule of thumb used to be 2% or so. With larger drives, this adds up to allot.

I generally leave 2%-5%. This equates to around 40-50G on a 1TB drive. This way if there is any kind of file system check operation which requires the space, then it is available for recovery.

On a 2TB drive I might go on the lower side of this. I would definitely not fill it to 100%

 

If I'm considering performance on a file system that is written to allot, then I hover between 75-85% usage, when you go over 90% on a file system that is written, performance can drag.

Read mostly, I go higher to 90%-95% usage.