topic Re: If link goes down, will there be a data loss in snapmirror schedule replication? in ONTAP Discussions

If link goes down, will there be a data loss in snapmirror schedule replication?

ATULPATHARE — Thu, 05 Jun 2025 06:51:19 GMT

Hi, I have two NetApp NAS servers installed at two different locations. I have set a snapmirror replication for a specific volume. and transfer schedule is set for after every 5 min all days. Initial synchronization is done and data is replicated. During the scheduled replication / transfer link between NAS went down after 2 min of transfer started. In first 2 min @ 106 MB data was transferred to destination NAS. But when i checked on the destination NAS the 106 MB data which was transferred before link goes down was missing. data replicated till last successful schedule replication was proper. I am not sure why this is happened. Is it the behavior of NetApp NAS? or is there any setting to avoid this data loss? Regards, Atul

Re: If link goes down, will there be a data loss in snapmirror schedule replication?

sowens — Fri, 01 Jul 2011 17:15:19 GMT

The behavior that you are seeing is expected.

For snapmirror replication, the entire transfer needs to complete before the data can be seen on the destination filer.

The high level steps for a SnapMirror transfer are:

1. The source storage system creates a Snapshot copy.

2. The new copy is compared to the baseline copy to determine which blocks have changed.

3. The changed blocks are sent to the destination and written to the file system.

4. After the update is complete, both file systems have the new Snapshot copy, which becomes the baseline copy for the next update.

In your case, step 3 was unable to complete due to the link break. In most cases, we would generate a restart checkpoint. Once the network link is re-established, the snapmirror transfer would start back from the restart checkpoint.