Data backup with rolling baselines

Techniques and components for backing up data are disclosed. A first subset of data units is selected from a plurality of data units of a storage system to create a first partial baseline for backup of the first storage system. The number of data units in the first subset of data units is determined based on a window size parameter n. Data within the storage system that has changed since a previous backup operation are identified. A first backup including the first partial baseline and the first changed data is written to a second storage system. For a data loss event, the techniques include selecting, based on a time of the determined data loss event in combination with n, the first backup and n−1 additional backups, wherein each of the n−1 additional backups include a partial baseline and changed data. The first backup and the n−1 additional backups are written to a third storage system.