Integrity verifier should support scanning a subset of volume's files

Think you have 500 GB of data in remote S3-compatible cloud storage.

Verifying all of that would cause you to use 500 GB of bandwidth, using 100 % of 10 Mbps network connection for five days straight. This will probably slow down the internet connection for everybody.

Because of this, it would be nice to be able to say that please verify only 10 % this week, next 10 % next week and so on.