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 backup disk space, use the following equations:

Without internal backup on the cluster

(full backup size * (number of full backups + 1)) + (incremental backup size * number of incremental backups)

With internal backup on the cluster

[(full backup size * (number of full backups + 1)) + (incremental backup size * number of incremental backups)] * 2

Creating a new backup does not remove the old backup, which is why there must always be enough space for an extra backup in addition to the total number of stored backups (number of full backups + 1).

Example

In this example we have the following input parameters:

  • 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 results of the backup space calculation – including headroom for an extra backup during backup creation – will then be:

Overall data volume (net) Full backup data size Incremental backup data size Backup space (without redundancy) Backup disk space required with redundancy

1200 GiB

1200 GiB (compressed data + indexes/statistical and auditing data)

2400 GiB

1200 GiB x 2

3600 GiB

1200 GiB x 3

6000 GiB

Full backup data size + Incremental backup data size

12000 GiB

Backup space (without redundancy) x 2 (this is calculated because the backups in this example are cluster-internal)

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.