Там сказано: the
old and
new being configuration prefixes in pdns.conf.
Ну т.е. заглядываете в pdns.conf и находите, что там как-то был прописан старый бекенд. Вот префикс оттуда и есть old. Там же по аналогии нужно прописать новый бекенд.
Дальше я воспользовался поиском:
https://yandex.ru/search/?text=pdns.conf+more+than...
перешел по ссылке
https://github.com/PowerDNS/pdns/blob/master/docs/...
и прочитал:
launch
Backend names, separated by commas
Which backends to launch and order to query them in. Launches backends. In its most simple form, supply all backends that need to be launched. e.g.
launch=bind,gmysql,remote
If you find that you need to query a backend multiple times with different configuration, you can specify a name for later instantiations. e.g.:
launch=gmysql,gmysql:server2
In this case, there are 2 instances of the gmysql backend, one by the normal name and the second one is called 'server2'. The backend configuration item names change: e.g. gmysql-host is available to configure the host setting of the first or main instance, and gmysql-server2-host for the second one.
Running multiple instances of the BIND backend is not allowed.
Т.е. у вас в конфиге должно быть что-то типа:
launch=gmysql,gmysql:server2
gmysql-host=192.168.1.1
gmysql-user=...
gmysql-password=...
gmysql-dbname=...
gmysql-server2-host=192.168.2.2
gmysql-server2-user=...
gmysql-server2-password=...
gmysql-server2-dbname=...
И тогда вы запускаете
pdnsutil b2b-migrate gmysql gmysql:server2