Recently, I’ve been taking part in discussions involving NetApp hardware and its backup solutions. When it comes to NetApp’s remote replication solutions SnapMirror and SnapVault, there can be confusion as to what each do and which best suits their needs. Although similar in name, SnapMirror and SnapVault differ in abilities and target different use cases, so let’s take a look at each to explore why both are important to consider.
SnapMirror aims to improve data availability through the mirroring of volumes between two NetApp sites. This is primarily a disaster recovery solution, which utilizes ONTAP Snapshots to keep the second site up to date with the primary site’s production data.
With SnapMirror, the user establishes a pairing between a read-write accessible production volume at the primary site and a read-only mirror volume from a secondary site. A SnapMirror pair can operate in one of three modes: Synchronous, Semi-Synchronous, or Asyncronous. The mode used will depend on what is possible and best suited for the situation. Synchronous keeps data between the primary and secondary site up to date but is generally for two sites that are physically close to each other such that latency is low and network bandwidth high. Asynchronous will span greater, global distances and will also enable interesting use cases such as cascading and multi-hop mirroring one-to-one, one-to-many, many-to-one, or many-to-many replication setups.
In all cases, at first setup of a SnapMirror link, an initial data transfer takes place from the source volume at the primary site to the read-only destination volume, so that these volumes start off with a copy of the same data. After, a Snapshot is created on the source volume from the primary site which is used to keep track of changes to this volume. Only changes are sent to the destination volume after the initial transfer, reducing network traffic which is also further reduced with compression. At scheduled time intervals, the Snapshot that is shared by both sites to keep track of changes is updated to a more recent Snapshot. At the end of every update, the previous Snapshot is removed and only the most recent Snapshot exists.
There are a few uses for SnapMirror, the most obvious being Disaster Recovery. Because a Snapshot is kept on the remote site, in the case of failure on the primary site not only does the user have the mirror volume on the secondary site to use as a temporary replacement but the most recent Snapshot also exists as a point in time to revert this volume back to.
SnapMirror can also be used for tape archiving and testing. Because a copy of the data from the primary site exists as a read-only volume on the secondary site, this secondary volume can be used to create a tape archive while having no impact on the production storage and applications. In addition, this secondary volume can be accessed to create a clone volume which can be used as an isolated snapshot of the production data for use in development and testing.
SnapMirror does many things well, but accomplishes these tasks with the assistance of one Snapshot through which to keep data updated at both sites of the SnapMirror volume pair. If instead you are looking for a solution to allow you to keep multiple Snapshot backups in a location remote from production data, then SnapVault is the right software for the job.
Initially, SnapVault establishes a link between a primary and remote site similarly to SnapMirror. SnapVault will create a full copy of the source data at the secondary site and take a Snapshot upon completion. According to a schedule set by the operator, SnapVault will create incremental Snapshots of the primary site’s data at the secondary site. These Snapshots are read-only and unlike SnapMirror will persist allowing you to have a backup history with multiple points in time. If needed, the data can also be restored from, using a restore command to restore a whole data set, or copying from the backup data via an NFS or CIFS mount. Due to this behavior, SnapVault is a great way to keep multiple point-in-time backups in their original, pristine state at a physically isolated location from the production data and primary site.
I hope that helps to clear up any confusion. In short, SnapMirror is primarily a Disaster Recovery solution which mirrors volume(s) at remote NetApp storage, while SnapVault is a backup solution that can hold backups from multiple points in time. If you have any questions or comments feel free to let us know in the comment section below.