I would like to suggest to configure a remote syslog server.

it centralizes all the log s and give you full control over the retention.

It would also avoid situation where a disk full would impact your logging as well XCP-ng or XOA host operations.

For your XCP-NG host go to you POOl, select Advanced tab and configure the Remote syslog host section to point to your syslog server.

For XOA, you can follow the instruction here :
https://docs.xen-orchestra.com/backups#send-xo-logs-to-an-external-syslog-server