QNAP Snapshot Reserve: Why 20% of Your Storage Pool Is Reserved
When you create a storage pool on QNAP QTS, 20% of its capacity is reserved for snapshots by default. This is a vendor setting you can change, and it significantly affects usable storage.
See exactly how much usable storage your configuration delivers.
What Is the QNAP Snapshot Reserve?
QTS uses a concept called snapshot space management. When you create a storage pool, QTS sets aside a portion of the pool's raw capacity specifically to hold snapshot data. By default, this is 20% of the pool.
This space is not visible to volumes as usable storage. It exists at the pool level, below the volume layer. Even if you never create a snapshot, the space remains reserved unless you explicitly reduce it.
How to Change the Snapshot Reserve
- Open QTS Storage & Snapshots
- Select your Storage Pool
- Click Manage (right-click or the action menu)
- Select Snapshot Space Management
- Change from percentage to a fixed size, or reduce to 0% if you do not use snapshots
Changes take effect immediately without requiring a pool rebuild or data migration.
Impact on Usable Capacity
On a 4-bay NAS with 4 × 8TB drives in RAID 5:
- Raw post-RAID capacity: approximately 21.8 TiB
- After 70 GB pool overhead: 21.7 TiB
- With 20% snapshot reserve: 17.4 TiB usable by volumes
- With 0% snapshot reserve: 21.7 TiB usable by volumes
The 20% reserve removes approximately 4.3 TiB in this example. Equivalent to a full 5TB drive.
Frequently Asked Questions
Can I recover space from an existing snapshot reserve without deleting snapshots?
If you reduce the snapshot reserve while snapshots exist, QTS will warn you that existing snapshots may be deleted if the new limit cannot accommodate them. Always check your snapshot retention policies before reducing the reserve.
Is the snapshot reserve used even if I have no snapshots?
The space is reserved (unavailable to volumes) regardless of whether snapshots exist. Reducing it to 0% makes all pool capacity available to volumes, but disables automatic snapshot storage. You can still create manual snapshots if space allows.