Running an Unscheduled
Checkpoints are recorded automatically every few seconds in the journal. These checkpoints ensure crash-consistency, and are written to the virtual machines journals by the Zerto Virtual Manager.
Each checkpoint has the same timestamp which is set by the Zerto Virtual Manager.
During recovery you pick a checkpoint in the journal and recover to this point. The crash-consistent checkpoints guarantee write order fidelity.
For Example:
If write A on a virtual machine in the VPG occurred before write B on a virtual machine in the VPG, then when a checkpoint is written, the journal will contain:
■ Neither of the writes
■ Both writes, and if they overlap the B data takes precedence
■ Only A – indicating the checkpoint occurred between A and B
The coordination is done by the Zerto Virtual Manager.
You can also integrate Microsoft Volume Shadow Copy Service (VSS) with Zerto Virtual Replication to ensure transaction consistency in a Microsoft Windows server environment.
You can also use a script to place the application in a quiesced mode, such as Oracle Hot Backup mode, and execute the Zerto Virtual Replication PowerShell cmdlet Set-Checkpoint, then release the quiesced mode. For more information about Zerto Virtual Replication PowerShell cmdlets, see Zerto Virtual Replication Cmdlets.
Note:
■ To write application-consistent checkpoints, there is a performance impact on the virtual machine running the application as a result of the application-consistent mechanism used, such as VSS. This is because the guest operating system and any integrated applications will be quiesced.
This impact on performance may be negligible and does not always happen since not all applications require these checkpoints in order to achieve successful application recovery. Also, Zerto Virtual Replication only requires the guest and application to quiesce for a brief moment, just long enough to add a checkpoint.
As previously mentioned, checkpoints are recorded every few seconds in the journal. After a while, the number of checkpoints available from which to choose a recovery point can be in excess of thousands per VPG.
When this threshold is reached, in order to enable efficient management and use of the checkpoints, the number of checkpoints is diluted with respect to time, as follows:
■ Within the latest 2 hours: All of the checkpoints are available for recovery.
■ Between 2 and ~4.5 hours: There are about two to three checkpoints every 15 minutes.
■ From 4.5 hours and over: 1 checkpoint is kept every 15 minutes.
Note: Checkpoints which are either added manually, or marked as part of a Failover test are not diluted.
Offsite Backup
After initializing the VPG, Zerto Virtual Replication periodically checks that the schedule to run an offsite backup - either daily or weekly - has not passed. At the scheduled backup time, the offsite backup is run and the offsite backup file stored in the specified repository.
To run an unscheduled offsite backup:
1. In the Zerto User Interface, click the VPGs or VMs tabs and select one or more VPGs to be backed up.
Note: You can also start from the OFFSITE BACKUP tab.
2. Click MORE > Run Backup.
Note: If the VPG was previously viewed, and the tab for this VPG is still displayed, you can access the details by selecting the tab.
3. Click OK.
The offsite backup starts. You can monitor the progress in the Offsite Backup tab and the tasks pane. During the backup job you cannot perform any other operation on the VPG without first aborting the job. You can start a live failover and you are then prompted to abort the job.
Scheduled backup runs for the VPG are skipped until the unscheduled run ends.
If the job runs out of the configured backup window, the virtual machines that are already stored in the repository are kept but remaining virtual machines in the VPG are not backed up. The job is reported as a partial backup.