Organization administrators use storage reservation to control whether they can allocate more storage than is available to databases in a database group. Administrators set a limit on how much storage can be overallocated.

Storage reservation determines the percentage of the total database storage allocation that is initially committed to the database group. The storage is reserved, although it is not used yet.

For example, if the organization administrator sets database storage at 100GBs and storage reservation at 20%, a total of 500GBs is allocated for all databases in the database group. If a user then creates one database in the group, the single database can allocate up to 500GBs of data storage but commit 100GBs. If a user instead creates five databases in the group, each database can allocate up to 100GBs of data storage but can commit 20GBs. You cannot add more databases to the group because all 100GBs are committed. For example, 500GBs are allocated, 100GBs are the capacity, and 400GBs are over allocated.