Provide the thin provisioning Device Mapper (DM) target and supporting userspace utilities. This DM target allows a single pool of storage to be the backing store of multiple thinly provisioned volumes. Numerous snapshots (and snapshots of snapshots) may be taken of the thinly provisioned volumes.
- Name: Joe Thornber and Mike Snitzer
- thornber AT redhat DOT com
- snitzer AT redhat DOT com
- Targeted release: Fedora 17
- Last updated: 2011-10-12
- Percentage of completion: XX%
The main highlight of this implementation, compared to the previous implementation of snapshots, is that it allows many virtual devices to be stored on the same data volume. This simplifies administration and allows the sharing of data between volumes, thus reducing disk usage.
Another significant feature is support for an arbitrary depth of recursive snapshots (snapshots of snapshots of snapshots ...). The previous implementation of snapshots did this by chaining together lookup tables, and so performance was O(depth). This new implementation uses a single data structure to avoid this degradation with depth. Fragmentation may still be an issue, however, in some scenarios.
Metadata is stored on a separate device from data, giving the administrator some freedom, for example to:
- Improve metadata resilience by storing metadata on a mirrored volume but data on a non-mirrored one.
- Improve performance by storing the metadata on SSD.