Veeam Backup & Replication

Backup Chain in Veeam Backup & Replication

A backup chain is a sequence of backup files created by backup jobs. The backup chain makes it possible to restore data. The backup chain includes the first full backup file, incremental backup files, metadata files, and some additional files. Full and incremental backup files are related to the restore points of the backed up virtual machines (VMs). You can think of recovery points as "snapshots" of virtual machine data at specific times. Restore points allow you to restore virtual machines to the desired state.

The type of backup files and how they are arranged in the backup chain depends on the backup method chosen. The number of backup chains for the backed-up virtual machines depends on the format of the backup chain chosen.

Backup Files

Veeam Backup & Replication creates and maintains different types of backup files:

• VBK — Full backup files that store complete copies of VM images virtual machines.
• VIB or VRB — Incremental backups that store incremental changes to VM images of virtual machines.
• VBM — Backup metadata files that store information about the backup job, virtual machines processed by the backup job, the number and structure of backup files, restore points, etc. Metadata files facilitate the import of backups, mapping backups, and other operations.

In addition to these file types, Veeam Backup & Replication can create the following files in the backup repository:

• VSB — Virtual synthetic backup files used to generate full virtual backups on tapes.
• VLB, VSM, and VLM—Files that store Microsoft SQL Server transaction log data.
• VLB, VOM, and VLM—Files that store Oracle log data.
• VLB, VPM, and VLM — Files that store PostgreSQL WAL data.

All backup files created by Job Backup are stored in a special folder related to Job in the backup repository. For example, if you create a backup job named "DC Backup", Veeam Backup & Replication will create a folder named "DC Backup" in the target backup repository and store all the backup files generated by this job in this folder.

Back to Rolling Back VMs

To return a virtual machine to a specific point in time, you need a chain of backup files: a full backup file plus a set of incremental backup files that depend on this full backup file. If some files are lost in the backup chain, you won't be able to revert to the desired state. For this reason, you should not manually delete individual backup files from the backup repository. Instead, you'll need to specify retention policy settings that allow you to maintain the desired number of backup files in the backup repository.

Backup Methods

Veeam Backup & Replication offers several ways to create backup chains:

Forever forward incremental incremental (FFI) incremental incremental backups

When the Perpetual Incremental Backup (FFI) method is used, Veeam Backup & Replication creates a backup chain that includes the first full backup file (VBK) and a set of Perpetual Incremental Backup (VIB) files that follow.

This backup method helps you save backup storage space, as Veeam Backup & Replication only stores a full backup file and deletes incremental backup files when the retention period ends. To comply with the retention policy settings, Veeam Backup & Replication imports the data from an increment file into the full backup file before the increment is deleted. These changes can lead to the fragmentation of the entire backup file, and you should plan the compression operation of the full backup file. This operation generates an additional I/O load on the backup storage. Overall, the FFI method has a modest impact on backup storage I/O compared to other backup methods.

Restoring to the first restore point from backup files created using the FFI method is the fastest compared to other methods, as the first restore point available is always a full backup. Recovery to other recovery points can be compared to the FI method in terms of speed.

Incremental Incremental Forward Backup (FI)

When the Forward Incremental Backup (FI) method is used, Veeam Backup & Replication creates a backup chain that includes multiple full backup files (VBK) and a set of forward incremental backup (VIB) files that are located after each full backup file. Full backups can be created using full synthetic and fully active backup methods. By performing regular full backups, the backup chain is broken down into shorter series. This reduces the chances of losing the backup chain entirely, making this backup method one of the most reliable.

This backup method requires more storage space compared to other methods because the backup chain contains multiple complete backup files, and sometimes Veeam Backup & Replication stores more than the number specified in the retention policy settings of restore points due to the FI retention policy features.

The FI method has the least impact on backup storage I/O. However, its impact on backup storage increases on days when full synthetic backups are scheduled, as does its impact on production storage on days when full active backups are scheduled.

Restoring from backup files created using the FI method is the most time-efficient compared to other methods (in cases where you do not return to the first or last restore point). This is because the backup chain is usually broken down into short series of full and incremental backup files, and it doesn't take much time to consolidate the desired restore point.

Reverse incremental (RI) backup

When the reverse incremental backup (RI) method is used, Veeam Backup & Replication creates a backup chain that includes a full backup file (VBK) and a set of reverse incremental backup (VRB) files that precede it.

This backup method helps you save backup storage space, as Veeam Backup & Replication only stores one full backup file (if full backups are not scheduled periodically) and deletes incremental backups when the retention period ends.

The RI method has the greatest I/O impact on backup storage compared to other backup methods. This is because during backup, Veeam Backup & Replication imports the changed data into the full backup file and also creates reverse incremental backup files. Such changes can lead to the fragmentation of the entire backup file, and you should plan the compression operation of the full backup file. This operation generates an additional I/O load on the backup storage.

Restoring to the last restore point from backup files created using the RI method is the fastest compared to other methods because the most recent restore point is always a complete backup that is updated after each backup cycle. Restoring to previous restore points is slower than other backup methods.

Forever Forward Incremental Backup

The Perpetual Incremental Backup (FFI) method generates a backup chain that includes the first full backup file (VBK) and a set of Perpetual Incremental Backup (VIB) files that follow.

Veeam Backup & Replication creates a perpetual incremental backup chain in the following form:

1. In the first backup job session, Veeam Backup & Replication creates a full backup file in the backup repository.
2. In subsequent backup job sessions, Veeam Backup & Replication only copies the data blocks of the virtual machine (VM) that have changed since the last backup session (full or incremental) and stores these blocks as an incremental backup file in the backup chain.
3. After a new restore point is added to the backup chain, Veeam Backup & Replication reviews the job retention policy. If Veeam Backup & Replication detects an obsolete restore point, it will change the backup chain to allow space for the most recent restore point.

To use the incremental backup method permanently, you'll need to select the following options in the backup job settings:

1. Select Incremental Incremental Backup Mode.
2. Disable full synthetic backups and full active backups. If you enable full synthetic backups and full active backups, Veeam Backup & Replication will generate an incremental backup chain going forward.

This method allows you to save only one full backup and then only save data changes, which saves storage space.

Forward Incremental Backup

The incremental backup method generates a backup chain that includes the first full backup file (VBK) and a set of forward incremental backup (VIB) files that follow. In addition, the incremental backup chain forward includes full synthetic backup files and active full backups, which divide the backup chain into shorter series.

Veeam Backup & Replication creates an incremental backup chain forward in the following form:

1. In the first backup job session, Veeam Backup & Replication creates a full backup file in the backup repository.
2. In subsequent backup job sessions, Veeam Backup & Replication only copies the data blocks of the virtual machine (VM) that have changed since the last backup session (full or incremental) and stores these blocks as an incremental backup file in the backup chain.
3. On days when full synthetic backups or full active backups are scheduled, Veeam Backup & Replication creates a full backup file and adds it to the backup chain. Incremental restore points that are generated after this full backup file use it as a new starting point.
4. After a new restore point is added to the backchain, Veeam Backup & Replication checks the retention policy set for the job. If Veeam Backup & Replication detects an outdated restore point, it will try to remove that point from the backup chain.

Incremental backups are the default way to create a backup chain with full synthetic backup enabled. To use this backup method, you can keep the default settings or select the following options in the backup job settings:

1. Incremental Incremental Backup Mode Selection
2. Enable full synthetic backup or full backup enabled. If full synthetic backups and full active backups are not enabled, Veeam Backup & Replication will generate an incremental backup chain permanently.

Reverse Incremental Backup

The reverse incremental backup method generates a backup chain that includes the last full backup file (VBK) and a set of reverse incremental backup (VRB) files that precede it.

Veeam Backup & Replication creates an inverse incremental backup chain in the following form:

1. In the first backup job session, Veeam Backup & Replication creates a full backup file in the backup repository.
2. In subsequent backup job sessions, Veeam Backup & Replication copies only the data blocks of the virtual machine (VM) that have changed since the last backup session and imports these blocks into the full backup file to bring it to the most recent VM state. In addition, Veeam Backup & Replication creates a reverse incremental backup file that contains the data blocks that were replaced when the full backup file was restored, and this adds the reverse incremental backup file before the full backup file in the backup chain.
3. After a new restore point is added to the backchain, Veeam Backup & Replication checks the retention policy set for the job. If Veeam Backup & Replication detects an outdated restore point, it removes it from the backup chain.

The result is that the most recent restore point in the backup chain is always a full backup, and it is updated after each successful backup session.

The reverse incremental backup method allows you to instantly restore a VM to the most recent state without the need for additional processing, as the most recent restore point is always a full backup file. If you need to restore a VM to a specific point in time, Veeam Backup & Replication applies the required VRB files to the VBK file to reach the desired recovery point.

To use the reverse incremental backup method, you need to select the Reverse incremental option in the backup job settings.

Switching Between Backup Methods

You can easily change the backup methods. Veeam Backup & Replication does not replace the previous backup chain, but rather creates a new backup chain alongside the existing chain in the following ways:

1. If you switch from the reverse incremental method to the incremental method permanently or incrementally forward, Veeam Backup & Replication creates a set of incremental backup files alongside the reverse incremental backup chain. The full backup file is used in the reverse incremental chain as a starting point for incremental backup files.
2. If you switch from the incremental method permanently or incrementally forward to the reverse incremental method, Veeam Backup & Replication will first create a full backup file next to the incremental backup files. In each new job session, Veeam Backup & Replication updates this full backup file and adds inverse incremental backup files to the backup chain.
3. If you switch from the incremental method permanently to the incremental method forward, Veeam Backup & Replication will create a full synthetic backup according to the specified timeline. When the number of restore points in the new chain reaches the maintenance limit, the old backup chain is deleted.
4. If you switch from incremental forward to incremental permanently, full synthetic backup will no longer be created. When the number of restore points created from the last full backup reaches the retention limit, the old backup chain is deleted. From then on, with each restore point creation, the initial incremental file will be merged with the full backup file.