How full should drive be?

[stepmback]

I have two 8 TB parity drives and 9 other disks. Some are 8TB and others are 3 TB and 4TB. All the 4 TB and 8 TB drives are about 90% full. Is there a best practice for how full you should let the drives get before I add another disk? Should I go past 90% on the 8 TB that is about 500GB of space left unused. 

[JonathanM]

I like to keep the cumulative free space close to the size of my largest data drive. That way if you need to juggle data around to clear off any specific disk you can.

 

How full any specific drive is allowed to get is determined by usage. Drives with seldom accessed and never updated content I fill to 95%, or so. I try to keep heavily used drives as empty as possible, whatever that may be.

 

Some free space can be useful for file system maintenance or repairs if needed. Filling to the last byte can be risky if something gets corrupted.

[stepmback]

I looked in Disk setting and see that I can set as a percentage the amount of space to leave. Is there a way to set the exact amount instead of a percentage? 10% of a 8 tb drive is a lot of space to leave open... While I am fine with leaving 10% on a 2 tb drive.

[trurl]

In Disk Settings, you can globally set warning and critical utilization, and in the Settings for each disk you can override those. But none of that does anything to prevent filling the disks, it just gives warnings and notifications.

 

Each user share has a Minimum Free setting. You should set Minimum to larger than the largest file you expect to write to the user share. When Unraid chooses a disk to write for the user share, it will choose a disk that still has more than Minimum.

 

And Minimum Free won't keep you from filling a disk either. If you set Minimum for a user share to 20G, and a disk has 25G remaining, the disk can be chosen, even if the file is 30G.

 

Unraid has no way to know how large a file will become when it chooses a disk for it.