What is the difference between a static volume, thin volume, and thick volume?
Applicable Products
- Storage & Snapshots
- QTS
Static Volumes
A static volume is a simple and easy-to-use volume which contains all the available storage capacity on the disks/RAID selected to create the volume. A static volume does not have a storage pool and does not support advanced storage features such as snapshots and Qtier. However, static volumes can still take advantage of SSD caching. A static volume is recommended for creating a simple, single volume that uses all the disks in your NAS, and you don’t need features like snapshots or Qtier. Also, due to its simplicity, the performance of a static volume is slightly better than other volume types.
Thin and Thick Volumes
Thin and thick volumes, also called flexible volumes, must be created inside a storage pool. A storage pool contains all the available storage capacity on the disks/RAID selected to create the pool. Once a pool has been created, flexible volumes can be created and will allocate storage space within the pool as required. Flexible volumes support advanced storage features such as snapshots, Qtier, and SSD caching.
Flexible volumes can also be resized, converted between thin and thick types, and backed up to a remote storage pool via Snapshot Replica.
Thin volumes allocate space in the storage pool as data is written into the volume. Only the size of data in the volume is used up from the pool space, and free space in the volume does not take up any pool space. If data is deleted from the volume, that space can be freed and given back to the storage pool free space. The pool free space is shared among all thin volumes, and the NAS administrator must take care to ensure there is enough free space in the pool as more data is written to thin volumes. In the event where there is insufficient pool space, thin volumes will enter read-delete or read-only mode until more pool space is available.
Thin volumes are recommended when you must create multiple volumes and share the storage pool space efficiently between them. Also, thin volumes are recommended if you are planning to use volume snapshots. When using snapshots with thin volumes, only modifications to existing data on the volume will increase the snapshot used space, the size will be the same as the modified data.
Thick volumes allocate the total size of the volume upon creation. No matter how much data is actually stored in the volume, the total size of the volume will always be used up in the pool. On the other hand, this space is guaranteed to be available exclusively for this volume, even if other volumes used up all remaining pool free space.
Thick volumes are recommended if you are creating multiple volumes but need to guarantee the space for a particular volume. The performance of a thick volume may also be slightly better than a thin volume in some situations.
The different space allocation behaviors between thick and thin volumes can be visualized in the following diagram:
Volume Type Comparison
| Volume Type | |||
|---|---|---|---|
| Static | Thick | Thin | |
| Summary | Best overall read/write performance, but does not support most advanced features | Good balance between performance and flexibility | Enables you to allocate storage space more efficiently |
| Read/write speed | Fastest for random writes | Good | Good |
| Flexibility | Inflexible A volume can only be expanded by adding extra drives to the NAS. | Flexible A volume can easily be resized. | Very flexible A volume can be resized. Also unused space can be reclaimed and added back into the parent storage pool. |
| Parent storage space | RAID group | Storage pool | Storage pool |
| Volumes allowed in parent storage space | One | One or more | One or more |
| Initial size | Size of the parent RAID group | User-specified | Zero Storage pool space is allocated on-demand, as data is written to the volume. |
| Maximum size | Size of the parent RAID group | Size of the parent storage pool | Twenty times the amount of free space in the parent storage pool The size of a thin volume can be greater than that of its parent storage pool. This is called over-allocation. |
| Effect of data deletion | Space is freed in the volume | Space is freed in the volume | QTS can reclaim the freed space and add it back into the parent storage pool. |
| Methods of adding storage space |
| Allocate more space from the parent storage pool | Allocate more space from the parent storage pool |
| Snapshot support (fast backup and recovery) | No | Yes | Yes |
| Qtier support (automatic data tiering) | No | Yes | Yes |
