Filter
Top Products
144 SANRAD V-Switch User Manual
Creating a Snapshot
You can create a snapshot, a point-in-time copy, of any volume at the top of a
hierarchy using the CLI command volume create snapshot. A
snapshot does not create a full copy of its source volume. It is a dynamic
and dependent volume that stores the original data from a source volume
when changes to the source volume are made after the snapshot’s creation.
Snapshot volumes use the copy old on write method, copying the old source
data to the snapshot and only then writing new data to the source volume.
Snapshots can be used for serverless backup, reducing the load on the
application server. The backup copy from a snapshot is a full copy of the
source volume at the time of the snapshot and adequate size must be
allocated for the backup volume. A snapshot can be built on any volume
hierarchy but, once created, cannot be used as a child in another volume
hierarchy. This means that a snapshot can be created on a mirror volume
with two children. However, after the snapshot is created, a mirror volume
cannot be created, using the snapshot as one of the children, to copy the
snapshot volume.
Figure 75, shows a source volume with its snapshot when the snapshot is
first created. Initially, a snapshot is empty because there has not yet been a
change in its source volume. Only when a write operation is performed on
the source volume will the snapshot begin to fill up.
10265
Snapshot1QA Testing
MM
AO
AS
NH
AN
SS
UN
PT
Figure 75. 1
st
Snapshot Created
Figure 76, page 145 shows the same source and snapshot volume after a
write operation to sector 1. The snapshot records the original data from
sector 1, S, to the snapshot and then the new data, B, is written to the source
volume.