Specifications

Using Snapshots
98 Snap Server Administrator Guide
Configuring third-party backup solutions
To configure a Snap Server to work with one of the supported backup solutions,
you must: (1) install the backup agent software on the Snap Server; (2) inform the
Snap Server of the IP addresses of each backup master server; and, (3) inform the
backup software of the Snap Server’s IP address. Instructions for these procedures
are given in “Third-Party Backup Applications” on page 153.
Tip
On a Macintosh computer, you must mount the appropriate shares (volumes)
on the desktop so that the Macintosh backup programs can operate without a
remote agent.
Using Snapshots
A Snapshot is a consistent, stable, point-in-time image of a volume used for backup
purposes. For the life (duration) of the Snapshot, before new data is written to the
live file system, the original data is written to the Snapshot, thus preserving the
original image. Snapshots consume a minimum of storage space because they
record only data that has changed.
How Snapshots Impact Performance
When a Snapshot is active, you may experience a slight drop in write performance
on new writes to the file system because the original data must be written to the
most recent Snapshot before any new data is written to the live file system.
Depending on the situation, the drop in write performance may range from five to
ten percent.
Snapshot Chaining
Chaining technology resolves both the storage cost and performance issues
formerly associated with Snapshots. Because each Snapshot ‘re-uses’ data from
more recent Snapshots, no space is wasted, and only one write to disk (for the most
recent Snapshot) is required to maintain all the Snapshots, regardless of how many
exist.
This dependency of newer Snapshots on all previous Snapshots means that when
you delete a Snapshot, all previously taken Snapshots are also deleted. Also, any
expired snapshots will not be deleted until the snapshot that has a dependence
upon it has expired, or is deleted. For example, if ten Snapshots currently exist (with
number ten being the most recent), and you delete Snapshot number five,
Snapshots one through four will lose the source of some of their data, rendering
them invalid, and thus the Snap Server deletes them as well.