My current backup strategy for our AlwaysOn clusters is a daily full backup and hourly transaction log backups via a third party backup program. We had a request to minimize the amount of log backups and I noticed that we had a cluster of large log backups at the same time during the day and we began a process to run a log backup to nul right before a full backup.
It seemed to have worked until I tried to do a point in time restore and then it wouldn't restore past the full backup. I investigated and noticed that there is an overlap in the LSN's being backed up. Here is an example for one of the databases.
Last real log backup (secondary) - 20165000011169700001 / 20168000018974100001 backup to nul (primary) 20168000018974100001 / 20168000019060800001 full backup (primary 20168000019060800001 / 20168000019245900001 first log backup (secondary) 20168000019060800001 / 20174000018926600001
It looks like like the log records backed up to the nul device isn't being registered on the secondary node of the cluster. I assumed that running backup log on any node will transfer to the other one since we normally run log backups on the secondary.
Is this how it is supposed to work?