Snapshot Size Calculator
Estimate the size of a storage snapshot based on source volume size, daily change rate, and days since the last snapshot.
Inputs
Percentage of the source volume's blocks that change per day
Estimated Snapshot Size
105.00GB
Daily Change Volume
15.00GB
Snapshot as % of Source Volume
21.0%
Step by step
Values used
Source Volume Size = 500 GB; Daily Data Change Rate = 3; Days Since Last Snapshot = 7
Snapshot size
size = min(source_size, source_size × daily_change% × days_since_last)
Estimated Snapshot Size
= 105.00 GB
Daily Change Volume
= 15.00 GB
Snapshot as % of Source Volume
= 21.0
How it works
Copy-on-write and redirect-on-write snapshots only store blocks that changed after the snapshot was taken, so snapshot size grows roughly linearly with the daily change rate multiplied by how many days have elapsed since it was created — the longer a snapshot is retained, the more accumulated changes it must track, until in the worst case it approaches the full size of the source volume (every block has changed at least once).
Formula
Snapshot size
size = min(source_size, source_size × daily_change% × days_since_last)
Frequently Asked Questions
Why does the calculator cap the snapshot at the source volume size?
A copy-on-write snapshot can never store more changed data than the source volume actually contains — once every block has been overwritten at least once since the snapshot was taken, the snapshot has effectively captured a full copy and further growth stops.
Why do old snapshots often cause storage alerts?
Because snapshot size grows with elapsed time, a snapshot left in place for weeks or months accumulates far more changed-block overhead than a short-lived one — this is why most storage platforms recommend deleting or consolidating snapshots on a schedule rather than leaving them indefinitely.
Does a higher daily change rate always mean the snapshot fills up faster?
Yes — the daily change rate is the dominant driver of snapshot growth; a volatile volume (databases, active VMs) with a high change rate will consume much more snapshot space per day than a mostly static volume (archives, templates), even at the same retention period.