What is the recommended free space on HFS+ volumes?

Maintain at least 20% free space on HFS+ volumes. When a volume is more than 90% full, performance can slow dramatically and the volume directory is more likely to become damaged.

To keep your volume healthy, regularly monitor available space and clear out unneeded files before reaching that threshold. Keeping sufficient free space gives HFS+ room to manage its directory structure efficiently and helps prevent file system errors.

Volume Full alert: SoftRAID will warn you when a volume exceeds 90% capacity. This is a proactive warning, not an error — but it should not be ignored. Clear space on the volume as soon as possible after receiving this alert.

Note: Very large HFS+ volumes may hit an allocation block limit, causing a “Volume Full” alert even when substantial free space appears to exist. This is a known HFS+ limitation related to the allocation block size being fixed at the time the volume was originally formatted. If this occurs, consider deleting and reformatting the volume as APFS, which does not have this limitation.