If the disk usage exceeds 90% of the volume capacity, the level indicator will turn red.
Especially on a volume that contains an installation of mac OS, we recommend that you try to maintain at least 10% of the volume as free space.
If the partition you want to expand is not the root partition, then you can simply unmount it and resize the partition from the instance itself.
If the partition you need to resize is the root partition for an instance, the process becomes more complicated because you cannot unmount the root partition of a running instance.
MBRs are not present on non-partitioned media such as floppies, superfloppies or other storage devices configured to behave as such.
When disk usage exceeds 70% of the volume capacity, the level indicator will turn yellow to indicate that you may want to consider "cleaning house".The Disk Center table in the sidebar displays a list of locally-attached, mounted volumes.Click on one of these volumes to display information such as the volume name, filesystem, capacity, and disk usage.You may just need to resize the file system on your volume to make all of the space available.If you are not sure if your volume has a partition that needs resizing, see To check if your volume partition needs resizing for more information.