amount of all accounts, containers, objects

There isn't a single call to get this info. The information is stored in each account, so you need to add up the information in each account to get a cluster-wide total.

Since Swift doesn't give you a listing of all the accounts in the system, you can either use your auth system to get an account listing (and then eg do a HEAD to each one) or you can walk the drives in the account ring and examine the on0disk account DBs.

You can use something like slogging (http://github.com/notmyname/slogging), which walks the drives and looks at log files to get this info. Or you can use Ceilometer, if you are using keystone. Ceilometer does a HEAD to each account and adds up the numbers.