In order to put together an Exasol business continuity plan, you need to establish what the Recovery Point Objective (RPO
Recovery Point Objective: The maximum database backup age.) and Recovery Time Objective (RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup.) are.
Recovery Point Objective (RPO)
The RPO forms the basis of the Exasol business continuity plan, because it answers the question, 'How much data can my business afford to lose?'. Essentially, the RPO is the point in time that you will be able to restore your system to after a disaster or outage.
An important factor for determining RPO is how your system handles input data, specifically whether or not input data can be stored for a period of time. There are two scenarios, based on how input data is handled:
Input data is not stored
All data that was generated between the start of the last successful backup and the disaster event is lost. The database will be restored to the same state that it was when the last successful backup started.
The RPO determines how much data can be lost, and therefore determines the maximum amount of time that can pass between the start of the last successful backup and a disaster event. This in turn determines how frequently backups should run.
Input data can be stored
In this scenario, input data can be stored for a certain amount of time, for example in external systems. This means that there is an added step for recovery: once the last backup has been recovered, all unloaded input transactions also need to be loaded in the database.
In these cases, the maximum backup age can be calculated using two factors:
- The amount of time that input transactions can be stored.
- How long backups take to be restored.
The following equation can be used to calculate the maximum backup age:
Max Backup Age = Input Data Storage Time - Backup Restore Time
For example, if input data can be stored a maximum of 8 hours, and a backup restore takes 2 hours to complete, then the maximum backup age should be 6 hours.
Backup restore time also includes time to access the backups, and to start the backup recovery process.
For both scenarios, the shorter your RPO Recovery Point Objective: The maximum database backup age. is, the less time can pass between backups. This could mean greater backup frequency, or even instant data mirroring. The strategy you select needs to be taken into account in your hardware and network planning.
Recovery Time Objective (RTO)
The RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup. you decide on answers the question, "What is the maximum amount of time the system can be down or at limited capacity?".
For an Exasol database, the RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup. is the duration of time from the point of disaster until the last successful database backup is restored. Note that this time period includes time it takes to access the backups, as well as time for the restore itself. If you are restoring several backups - such as a full backup and several incremental backups - the entire time for the restore must be taken into account.
The time taken for decision-making after a disaster (for example, deciding whether or not to do a restore) should not form part of the RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup..
Depending on your backup strategy, it might be possible to do a non-blocking restore of an Exasol database. Although this is slower than a blocking restore, a non-blocking restore makes it possible to use the system at a reduced capacity while the data restore is taking place.
Interrelatedness of Factors
The complexity of devising any business continuity plan lies in the inter-relatedness of the variables involved. Below are just some of the factors that are interrelated.
- RPO and RTO:
These two concepts are closely linked. Specifically, the RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup. you define determines the maximum amount of time that you have to restore the last successful backup. This influences the RPO Recovery Point Objective: The maximum database backup age., which determines the maximum database age.
- RPO/RTO and Backup Strategy:
The RTO takes into account the amount of time required for a backup restore. The restore time depends on the size of the backups, which is determined by the backup frequency, and how many backups (full and incremental) there are to restore. A shorter RTO Recovery Time Objective: The duration of time from the disaster event until Exasol is up and running with data from the last successful backup. means that backups have to be more frequent, and that the RPO Recovery Point Objective: The maximum database backup age. is not so far back in the past.
