The recommendation of 5% free space comes from arrays in sizes of 100s of GB, not tens of TB.
This is the same kind of issue that Linux root filesystems had - a % based limitation made sense when disks were small, but now they don't make a lot of sense anymore when they restrict usage of hundreds of GB (which are not actually needed by the filesystem to operate).
This is the same kind of issue that Linux root filesystems had - a % based limitation made sense when disks were small, but now they don't make a lot of sense anymore when they restrict usage of hundreds of GB (which are not actually needed by the filesystem to operate).