To reduce I/O operations and associated costs, Veeam Backup & Replication will automatically add 10 days to the immutability expiration date. This period is called Block Generation. You do not have to configure it, the Block Generation setting is applied automatically. For example, if you set your immutability period to 30 days for your object storage repository, Veeam Backup & Replication will add 10 days to specific objects to reduce I/O operations with the data blocks over time. Thus, you will have immutability set for 30 days + 10 days of Block Generation set for data blocks in your object storage repositories.
How Block Generation Works
When the first data block (a full backup) arrives, its immutability period by default is set to 30 + 10 = 40 days. The first full backup starts its generation, that will be appended with the incremental backups. All the incremental backups within the generation (that is, within the 10-days period) will have the same immutability expiration date as the full backup. For instance, a data block that was offloaded on day 9 will have the same immutability expiration date as a data block offloaded on day 1. Thus we ensure that the immutability period for all the data blocks within a generation is no less than 30 days.
To maintain the backup consistency, Veeam Backup & Replication can extend immutability expiration for all data blocks in all backup chains (both active and inactive) and assign these blocks to a new generation. For example, within one forward incremental backup chain, a full backup file can not be removed before an incremental backup file. On the other hand, an incremental backup file makes no sense without relevant full backup file. So the immutability period is extended for all data blocks in the backup chain.
With 10 days of immutability automatically added, it means there is no need to extend the immutability period for the incremental backups in forward chain and for the unchanged blocks of current full backups in reverse chain offloaded within those 10 days. On the 11th day, though, the immutability period will have to be extended (to ensure that the immutability period for all the data blocks within a generation is no less than 30 days).
Consider the following: