SnapMirror replicates data from one volume (the source) to another volume (the mirror) and periodically updates the mirror to reflect incremental changes on the source. The result of this process is an online, read-only volume (the mirror) that contains the same data as the source volume at the time of the most recent update.
Note: SnapMirror requires a license code.
To use SnapMirror, you create an offline volume to be used as the destination for data replication. The destination volume is referred to as the "mirror." The mirror can reside on the same filer as the source volume or on another filer.
The source volume and the mirror volume must be of the same volume type. For example, if the source is a traditional volume, the volume you create to be its mirror must be another traditional volume.
To replicate data for the first time, the filer transfers all data in all snapshots in the source volume to the mirror. After the filer finishes transferring the data, it brings the mirror online. This version of the mirror is the baseline for future incremental changes.
To make incremental changes on the mirror, the filer takes regular snapshots on the source volume according to the schedule specified in the /etc/snapmirror.conf file. By comparing the current snapshot with the previous snapshot, the filer determines what changes it needs to make to synchronize the data in the source volume and the data in the mirror. For example, if a file is deleted from the source volume, SnapMirror deletes the corresponding file in the mirror the next time it updates the mirror.
After you replicate a volume, the active file system and all snapshots in the source volume are available on the mirror. As with any volume, you can export the mirror for NFS mounting or add a share corresponding to this volume for CIFS sharing.
SnapMirror makes all changes to the mirror at the same time. If you have an open file in the mirror while the filer is updating the mirror, you do not see the changes immediately. After the mirror update is finished, if you open the file, you see the changes. This is similar to the situation in which another user changes a file in a regular volume when you are reading the file: you can see the changes the next time you open the file.
The following list describes the differences between a mirror and a regular volume:
A mirror has snapmirrored status, which means that it contains read-only data and network clients cannot write data to the mirror.
The filer does not create automatic snapshots on the mirror based on the snapshot schedule.
You cannot create qtrees on a mirror; however, if qtrees exist in the source volume, the filer mirrors the qtrees to the mirror.
You cannot enable quotas on a mirror.