I am trying to set up Ola Hallengren maintenance backups on a 3 node cluster with each backup in an availability group, using a unc path as backup directory. I have specified the back up path \Serverbck\backups\ in the script as the directory however when I created the job and specify that same backup path the job runs but I cannot see anything in that location. I have also created a folder for the back up \Serverbck\backups\servername\instancename\fullbackup but nothing still, any help.?
If you are backing up to a UNC path the SQL Server service account needs to have rights to the share. (ie The actual backup is done by SQL Server, not the agent.) This is true whether or not you use Ola Halengren's routines.
Ola's utility will utilize the backup preference setting for the AG. That means - running the backup on the primary node when you have preferred secondary or secondary only selected as the backup preference means no backups will be done on the primary node for any databases in the AG.
Databases that do not participate in the AG will be backed up. If you are using the parameter AVAILABILITY_GROUP_DATABASES in the command and trying to run on a node that is not defined as the preferred node - nothing will be backed up.
Since this is a 3-node cluster you also have to consider the preference order. If all nodes are set to 50 (for example) and the option is to prefer secondary - then either of the secondary nodes can be defined as the preferred secondary.
Ensure the SQL Server service account has appropriate permissions to access the UNC path \\Serverbck\backups\. Verify that the network share is accessible from all cluster nodes and check the job history for any related errors.
The UNC you're using is posted as "\Serverbck\backups". That's incorrect.
It should be "\\Serverbck\backups" (has two backslashes before the machine name in the UNC). Of course, that might be because of this forum software but have to make sure.
As the others stated, SQL Server must also have privs to write there.