Release Notes

14 Dell PS Series Snapshots and Clones: Best Practices and Sizing Guidelines | BP1027
new data from cache to the physical disks. Reducing unnecessary workload on the disks reduces latency and
results in more available resources for the system to meet an application’s requirement.
Snapshot changes
Snapshot reserve can never grow beyond 100% of the base volume for a single snapshot. However, if there
are multiple snapshots, the reserve usage may be greater than the size of the base volume. This usage
depends on the actual change rate and I/O pattern occurring on the base volume and how many snapshots
are retained.
The following example explains sharing pages of data between multiple snapshots of a base volume:
1. Assume that the base volume occupies four pages of data. At time 0, the user takes the first snapshot
(snapshot 0). Since there are no changes to the base volume, the first snapshot and the base volume
point to the same logical page of data (refer to Figure 3).
2. When data changes, for example an application writes new data, the base volume pointers are
updated to the new pages and the first snapshot continues to point to the original data (refer to Figure
4).
3. A second snapshot is created (snapshot 1) capturing the changes made after snapshot 0. However,
changes made after snapshot 1 will be captured on a subsequent snapshot (Figure 5).
Base volume and snapshot 1
Depending on the number of snapshots and the amount of changes made to the base volume, the snapshot
reserve space can exceed the total allocated space. If the snapshot reserve is entirely consumed, the default