Current overwriting policy is shown as below.

If disk free space reaches the lower bound, the system would do the following steps.

1. Delete alarm recordings older than the preserved days (if you did not set yet, the
   value is 0) utill space becomes enough.
2. If not enough, delete normal recordings until space become enough.

So, if you did not set reserved days of alarm recordings, all alarm recordings would be almost deleted after overwriting.