axiom-storage-management-ref

# iOS Storage Management Reference

**Purpose**: Comprehensive reference for storage pressure, purging policies, disk space, and URL resource values
**Availability**: iOS 5.0+ (basic), iOS 11.0+ (modern capacity APIs)
**Context**: Answer to "Does iOS provide any way to mark files as 'purge as last resort'?"

## When to Use This Skill

Use this skill when you need to:
- Understand iOS file purging behavior
- Check available disk space correctly
- Set purge priorities for cached files
- Exclude files from backup
- Monitor storage pressure
- Mark files as purgeable
- Understand volume capacity APIs
- Handle "low storage" scenarios

## The Core Question

> **"Does iOS provide any way to mark files as 'purge as last resort'?"**

**Answer**: Not directly, but iOS provides two approaches:

1. **Location-based purging** (implicit priority):
   - `tmp/` → Purged aggressively (anytime)
   - `Library/Caches/` → Purged under storage pressure
   - `Documents/`, `Application Support/` → Never purged

2. **Capacity checking** (explicit strategy):
   - `volumeAvailableCapacityForImportantUsage` — For must-save data
   - `volumeAvailableCapacityForOpportunisticUsage` — For nice-to-have data
   - Check before saving, choose location based on available space

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## URL Resource Values for Storage

### Complete Reference Table

| Resource Key | Type | Purpose | Availability |
|--------------|------|---------|--------------|
| `volumeAvailableCapacityKey` | Int64 | Total available space | iOS 5.0+ |
| `volumeAvailableCapacityForImportantUsageKey` | Int64 | Space for essential files | iOS 11.0+ |
| `volumeAvailableCapacityForOpportunisticUsageKey` | Int64 | Space for optional files | iOS 11.0+ |
| `volumeTotalCapacityKey` | Int64 | Total volume capacity | iOS 5.0+ |
| `isExcludedFromBackupKey` | Bool | Exclude from iCloud/iTunes backup | iOS 5.1+ |
| `isPurgeableKey` | Bool | System can delete under pressure | iOS 9.0+ |
| `fileAllocatedSizeKey` | Int64 | Actual disk space used | iOS 5