Dell PowerVault 720N, Command Reference Manual, Page: 265 / 606

Snapshots 9-13
‡
The first number is equal to
‡
The second number is equal to
7KH7RWDO&ROXPQ
The %/total column shows space consumed as a percentage of total disk space in
the volume.
‡
The first number is equal to
‡
The second number is equal to
“Cumulative snapshot space” is the total space used by this snapshot and all
other more recent snapshots (the ones preceding this snapshot in the
snap
list
output).
2XWSXW6XPPDU\
The %/used number is more useful for planning the snapshot reserve because it is
more likely to remain constant as the file system fills.
The example shows a volume that keeps five nightly snapshots and four hourly snap-
shots. That is, the volume uses the following command for creating snapshots
regularly:
snap sched vol0 0 5 4@8,12,16,20
The
snap list
output shows that the overhead for snapshots is only 10%, so the
default snapshot reserve of 20% seems to be a waste of disk space. Assuming that
this pattern of change holds up, a reserve of 12% to 15% provides a safe margin to
ensure that removing files frees disk space when the active file system is full.
The values in parentheses, that is, the values that show the space used by an individ-
ual snapshot, are useful in identifying a particular snapshot to remove when the file
system is full. However, deleting a particular snapshot doesn’t necessarily release the
total amount of disk space indicated, because other snapshots might be referring to
the same blocks. Refer to “Adjusting Disk Space Used by Snapshots” for further infor-
mation about how to select a snapshot file for deletion to reclaim disk space.
cumulative snapshot space x 100%
cumulative snapshot space + file system space
this snapshot x 100%
this sn file system space
cumulative snapshot space x 100%
total disk space in this volume
this snapshot x 100%
total disk space in this volume