Source cleaning cascaded volumes using write and background copy indicators

A method comprising:

• storing a primary volume and a plurality of cascaded backup volumes for the primary volume;
• determining whether a write to one of the backup volumes is due to a background copy being made of another volume in the cascade;
• adjusting a background copy indicator in a volume map for the backup volume if the write is due to a background copy of another volume in the cascade;
• determining whether a write to one of the backup volumes is due to a write to another volume in the cascade;
• adjusting a write copy indicator in a volume map for the backup volume if the write is due to a write to another volume in the cascade;
• determining whether one of the backup volumes in the cascade should be cleaned;
• determining, if a backup volume should be cleaned, whether a write copy indicator for a region of the volume to be cleaned is marked in the volume's volume map;
• selecting another region to analyze if the write copy indicator for the region is not marked in the volume's volume map;
• determining, if the write copy indicator for the region is marked in the volume to be cleaned's volume map, whether a write copy indicator for the region is marked in a volume map for a downstream volume in the cascade;
• selecting another region to analyze if the write copy indicator for the region is marked in the downstream volume's volume map;
• and
• copying, if the write copy indicator for the region is not marked in the downstream volume's volume map, the region's data from the volume being cleaned to the downstream volume.