A company has a vault relationship between ClusterA and ClusterB. After a month of operations, the SnapVault update fails. The primary and secondary volumes have been thin provisioned and are…

The question explicitly states that both the primary and secondary volumes report available space, which confirms the primary aggregate is not full and cannot be the cause of the transfer failure.

Available space was confirmed on both volumes by the question, ruling out a full secondary aggregate as the root cause of the SnapVault update failure.

ONTAP cluster peering relationships depend on authenticated trust between clusters. If the cluster peer authentication passphrase or credential is not refreshed before it expires, the peering relationship becomes invalid and SnapVault update transfers fail even when connectivity exists. Re-establishing or refreshing the cluster peer authentication restores the trust relationship and allows SnapVault updates to resume.

While ONTAP does enforce a snapshot limit on SnapVault destinations, after only one month of standard operations the destination snapshot count would typically be far below the 251-copy limit, making this an unlikely cause given the scenario described.