When the logical space enforcement feature is enabled, ONTAP counts the logical-used blocks in a volume to determine the amount of available space that is still available in that volume. If there is no space available in a volume, the system returns an ENOSPC (out-of-space) error message.
Logical space enforcement ensures that users are notified when a volume is full or nearly full. Beginning with ONTAP 9.5, logical space enforcement returns three types of alerts to inform you about the available space on a volume:
This alert tells you that adding to the size of the volume might not create available space since that space will already be consumed by overallocated logical blocks.