Purgeable Space Internals
Also known as: purgeable space ios, reclaimable storage
Purgeable space is storage iOS counts as in-use but can automatically reclaim when the disk fills. It is made of caches, temporary files, and offloadable content the system can regenerate or re-download, so free space and purgeable space together form the true headroom available for new data.
- Purgeable space is counted as used but auto-deleted by iOS when the disk fills.
- It is reported through volumeAvailableCapacityForImportantUsage on APFS volumes.
- Apps cannot trigger purging directly; the system reclaims it on write pressure.
What purgeable space is
On an APFS volume, iOS classifies storage into used, free, and purgeable. Purgeable bytes are data the system has decided it can delete on demand without losing anything the user cannot recover, such as NSCachesDirectory contents, temporaryDirectory files, streamed media, and locally-optimized photos backed by iCloud.
The OS reports this via the `volumeAvailableCapacityForImportantUsage` key on URLResourceValues. Crucially, an app that asks how much room it has for a large import receives free space plus purgeable space, because the system will silently evict purgeable data first.
How iOS reclaims it
Reclamation is automatic and opaque. When a write would otherwise fail for lack of space, iOS purges in priority order: app URLCache and caches directories, then tmp files, then optimized-photo originals it can re-fetch from iCloud, and other regenerable system content. The user never confirms this and apps cannot schedule it directly.
This is why a device can show tens of gigabytes of "System Data" or "Other" that shrinks on its own under pressure. It also means freeing space by deleting caches may show no immediate change in the Settings storage bar, since those bytes were already counted as purgeable.
Why it matters for cleanup
A storage cleaner cannot force iOS to purge, and it should not promise that deleting app caches yields a one-to-one gain, because some of that data was already purgeable. The durable wins come from removing genuinely user-owned, non-regenerable data: duplicate photos, large videos, and unneeded files.
Cleanor focuses on that real, user-controlled footprint. The purgeable layer is the operating system's own safety valve, and the most reliable way to keep it from constantly thrashing is to lower the underlying usage rather than to fight the cache.