Backup Disk Space Calculation
This section explains how to calculate the required disk size for backups.
Exasol provides two types of backup: full backup and incremental backup. The backups can either be stored internally within the cluster or written directly to an external backup storage. Cluster internal backups will be stored redundantly to ensure that there is still a valid backup even in case of a node failure. If you use external storage, no backup redundancy is required.
A typical backup cycle is:
- Sunday: full backup with 10 days retention time
- Monday to Saturday: incremental backup with 3 days retention time
The size of incremental backups can vary depending on the change rate of your database, which can be difficult to predict. To ensure that there is enough disk space in the cluster, calculate with the maximum incremental backup size. Alternatively, you can calculate only with full backups (5 backups) to have a comfortable headroom as for disk space in the cluster.
Calculate Backup Disk Space
To calculate the required disk space for backups, use one of the following equations depending on your backup configuration:
Backups are stored outside of the cluster (remote backups)
(full backup size * (number of full backups + 1))
+ (incremental backup size * number of incremental backups)
= Required backup disk space
Backups are stored in the cluster (local backups)
((full backup size * (number of full backups + 1))
+ (incremental backup size * number of incremental backups)) * 2
= Required backup disk space
Creating a new backup does not remove the old backup. Because of this, there must be headroom for an extra backup during backup creation in addition to the total number of stored backups (number of full backups + 1).
Example
In this example we have the following input parameters:
- Total net data volume: 1200 GiB
- Number of full backups: 2
- Number of incremental backups: 3
- Maximum incremental backup size: 100% of full backup
- Cluster-internal backup: Yes
- Backup redundancy: 2
The backup space calculation (including headroom for an extra backup during backup creation) will then be as follows:
| Parameter | Value | Explanation |
|---|---|---|
| Total data volume (net) | 1200 GiB | Compressed data + index volume + statistical and auditing data |
| Full backup data size | 2400 GiB | Total data volume (net) × 2 |
| Incremental backup data size | 3600 GiB | Total data volume (net) × 3 |
| Required backup disk space without redundancy | 6000 GiB | Full backup data size + Incremental backup data size |
| Required backup disk space with redundancy | 12000 GiB |
Required backup disk space without redundancy × 2 |
Because different versions of an object can be accessed my multiple queries run by different users, the backup can be larger than the physical layout of the objects themselves. We recommend that you include additional space to allow for this in the archive volume.
