Veeam Backup & Replication creates and maintains the following types of backup files:
- VBK — full backup files that store copies of full VM images.
- VIB or VRB — incremental backup files that store incremental changes of VM images.
- VBM — backup metadata files that store information about the backup job, VMs processed by the backup job, number and structure of backup files, restore points, and so on. Metadata files facilitate import of backups, backup mapping and other operations.
In addition to these file types, Veeam Backup & Replication can create the following files on the backup repository:
- VSB — virtual synthetic backup files used for generation of virtual full backups on tapes. For more information, see Virtual Full Backups.
- VLB — files that store transaction logs data. For more information, see Microsoft SQL Server Logs Backup and Restore and Oracle Logs Backup and Restore.
All backup files created by the backup job reside in a dedicated job folder on the backup repository. For example, if you create a backup job with the DC Backup name, Veeam Backup & Replication will create the DC Backup folder on the target backup repository and store all backup files produced with this job in this folder.
Backup files make up a backup chain. The backup chain consists of first full backup file, incremental backup files and, additionally, backup metadata file. Full and incremental backup files correspond to restore points of backed up VMs. You can think of restore points as of "snapshots" of VM data at specific points in time. Restore points let you roll back VMs to the necessary state.
To roll back a VM to a specific point in time, you need a chain of backup files: a full backup file plus a set of incremental backup files dependent on this full backup file. If some file in the backup chain is missing, you will not be able to roll back to the necessary state. For this reason, you must not delete separate backup files from the backup repository manually. Instead, you must specify retention policy settings that will let you maintain the desired number of backup files on the backup repository.
Veeam Backup & Replication offers 3 backup methods to create backup chains:
- Forever forward incremental backup
- Forward incremental backup
- Reverse incremental backup
By default, during every backup job session Veeam Backup & Replication writes data of all VMs to the same backup file. If necessary, you can instruct Veeam Backup & Replication to create per-VM backup chains — that is, produce a separate backup chain for every VM added to the backup job.