DAS Snapshots

A number of Linux distributions include snapshot technology. RedHat Enterprise Linux 4 which includes LVM ("Logical Volume Manager") is a good example. LVM is a file system management layer that can be placed on top of common file systems including XFS and Reiser.

A "snapshot" is a record of what the file system looked like at a particular moment in time. Once a snapshot is taken, the file system keeps a record of subsequent changes, so that the user can view both the state of the file system when the snapshot was taken and also of course can continue to view the current "live" state. This short article (http://kbase.redhat.com/faq/FAQ_80_3640.shtm) provides some additional information.

Snapshots are commonly used to assist with backup and recovery - the snapshot can be backed up, rather than the live system, to ensure consistency. However, that is not necessary for the PostPath Server™ - it is equally valid to backup the live server as to backup a snapshot.

What may be more useful when administering the PostPath Server™ is to use snapshots as a short-term temporary backup. For instance, suppose the system is configured to take a snapshot every twelve hours and to keep the four most recent snapshots available at any given time. If a user accidentally deletes a message, the PostPath Backup and Restore tool can directly browse a recent snapshot and restore the lost message to the live file store while the server continues uninterrupted.