To use SnapMirror for replicating a volume, use the vol snapmirror command set and two configuration files: /etc/snapmirror.conf and /etc/snapmirror.allow. The command set is described in "Replicating a volume." The configuration files are described in "The /etc/snapmirror.allow file" and "The /etc/snapmirror.conf file."
To use SnapMirror, you create an off-line 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.
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 on-line. This version of the mirror is the base line 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.
For more information about how SnapMirror uses snapshots to transfer data from the source volume to the mirror, refer to "Snapshots created during data replication."
When SnapMirror transfers data from one volume to another, it generates two volume copy operations in the same way as the vol copy command. Refer to "Volume copy operations" for the meaning of a volume copy operation.
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 where 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:
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Part No. 210-02334
File: mirror2.htm
Last updated: 04/26/99 08:11:54