ext2/3/4 by default has 5% of the filesystem capacity reserved for the root user
If that is what you mean and if that is what causes the “red” warning even though the drive still has got free space available
you can tune the filesystem to not reserve as much space for root only
man tune2fs
look at the explanation for the -m switch
5% reserved for root space doesn’t make much sense for a non system partition - and even there 5% is way too much with todays large drives.
(5% of 1TB is 50GB of unusable space except for root - when even 1GB likely is plenty of safety margin)
Set it to 1% or even lower with: tune2fs -m1 /dev/sdXy
or even set it to zero for a non-system drive
Then you can fill up the filesystem up to the brim (or near to it).
It gets inefficient when you get near that mark - and when the file system is full you have to deal with it yourself (by deleting files to re-gain some space).
Quotas are not implemented by default AFAIK
and these would not be affected by the default reserved block percentage of 5% for root
again, AFAIK.