PostgreSQL 12 High Availability Cookbook - Third Edition

Using LVM snapshots

One of the reasons we created a second layer of LVM on top of DRBD was to provide filesystem snapshot capabilities. When we create a snapshot, all the files on a particular volume will appear static on that snapshot until one of the following two things happens:

• We destroy the snapshot.
• The changes to the source volume are larger than the space we reserved for the snapshot.

This is the primary reason we left 5 percent space unused within our PostgreSQL volume group. If we create a snapshot, up to 5 percent of the database can change before we have to remove it. For larger storage devices, this should give us a lot of time to perform emergency restores, create byte-stable backups, or any other operation that requires ...