How the snap list output is calculated

The snap list output is calculated in a number of ways.

The %/used column shows space consumed by Snapshot copies as a percentage of disk space being used in the volume. The first number is cumulative for all Snapshot copies listed so far, and the second number is for the specified Snapshot copy alone.

The first number is equal to
The second number is equal to

The %/total column: The %/total column shows space consumed by Snapshot copies as a percentage of total disk space (both space used and space available) in the volume.

The first number is equal to

Cumulative Snapshot space is the total space used by this Snapshot copy and all other more recent Snapshot copies (the ones preceding this Snapshot copy in the snap list output).
The second number is equal to

Summary of the snap list command output: The %/used number is useful for planning the Snapshot reserve because it is more likely to remain constant as the file system fills.

The information shows a volume that keeps five nightly Snapshot copies and four hourly Snapshot copies.

The sample output shows that the overhead for Snapshot copies is only 10%, so the default Snapshot reserve of 20% seems to be a waste of disk space. If this pattern of change holds, a reserve of 12% to 15% provides a safe margin to ensure that deleting files frees disk space when the active file system is full.

The values in parentheses, which show the space used by an individual Snapshot copy, are useful in identifying a particular Snapshot copy to delete when the file system is full. However, deleting a particular Snapshot copy does not necessarily release the amount of disk space indicated, because other Snapshot copies might be referring to the same blocks.

Parent topic: Displaying Snapshot disk consumption statistics

Related concepts

What the Snapshot reserve is