During initial setup you gave Arq a budget for S3 storage. To edit the budget, open "Preferences" (from the "Arq" menu) and select the "Budget" tab.
You can enter the budget number in either dollars/month or GB.
Arq Agent periodically calculates the total storage being used in S3 for your computer's backups. If the total is over the budget, Arq Agent drops the oldest backups across all backed-up folders until the storage is within the budget.
NOTE: Arq Agent always keeps at least 1 backup of each folder, even if that means the storage is over budget.
When Arq Agent finishes dropping old backups, it deletes any S3 objects that are no longer referenced by any backup version.
During the budget enforcement process, Arq Agent checks to make sure that all objects referenced by backups are still in your S3 data. Objects could be missing if you've accessed your S3 data using some other app and deleted objects.
If an object is missing, Arq drops the backup version. If it's the newest backup version for the folder, Arq will create a new backup for that folder during the next backup cycle.
During the backup process, Arq Agent combines small files into "packs" before uploading them to S3, dramatically reducing the amount of network overhead and speeding the backup process.
After enforcing the budget and deleting unreferenced S3 objects, some packs may contain lots of objects that are no longer referenced by any backup version. Arq Agent combines the sparsely-used packs, reducing S3 space usage.