How much space does a snapshot use?
This information is not Operating System specific
Snapshots are a feature in the GuardianOS. A Snapshot is a consistent, stable, point-in-time image of a volume used for backup purposes. Note this does not replace backing up data to an external medium. For the life (duration) of the Snapshot, before new data is written to the live file system, the original data is written to the Snapshot, thus preserving the original image. Snapshots consume a minimum of storage space because they record only data that has changed.
Estimating Snapshot Pool Requirements
Snapshot data grows dynamically for as long as a snapshot is active and as long as there is enough space available in the snapshot pool to store them. When the snapshot pool approaches its capacity (at about 95 percent), the SnapServer deletes the oldest snapshot's data to create space for more recent snapshot data.
The default configuration allocates 80 percent of RAID capacity to the volume and 20 percent to the snapshot pool. The size of the pool up (assuming unallocated space exists) can be adjusted according to your needs. If the snapshot strategy does not require all of the space allocated to the snapshot pool by default, consider decreasing snapshot pool capacity and re-allocating the capacity to the file system. To adjust the size of the snapshot pool, navigate to the Storage > Snapshots screen, and click the Adjust Snapshot Space link in the introductory text.
The number of snapshots that a RAID can support is a function of these factors:
(1) the space reserved for the snapshot data;
(2) the duration of the snapshots;
(3) the amount and type of write activity to the volume(s) since the snapshot was created.
The following table describes minimum and maximum allocation cases.
Guidelines for Estimating Snapshot Pool Requirements
Allocate about 10% of RAID if:
-- Activity is write-light
-- Write access patterns are concentrated in a few places<
-- A small number of Snapshots must be available at any point in time
Allocate about 25% of RAID if:
-- Activity is write-heavy
-- Write access patterns are randomized across the volume
-- A large number of Snapshots must be available at any point in time