How can I generate a list of clients and backups for one month with dump_root_hashes.rb script

You can use the --before and --after flags to limit the timeframe of the backup queries. These flags accept a variety of date formats but I usually use ISO 8601 dates because they're clear and unambiguous.

Alternatively, you could import the CSV into a spreadsheet application and either filter by date or use a pivot table. This is how I normally work with the data.

dump_root_hashes will show you the pre-dedupe size for each backup as recorded in the backup records. Trying to sum those values doesn't really make sense.

What is it you're trying to do?

Thank you for your information. I ran that script with --before and --after flags (for 1 month) but when I check data usage, . It shows 99 TB for one month. It looks like not right data