SnapProtect - SnapProtect for Open Systems C-Mode - Getting Started – NetApp

SnapProtect for Open Systems C-Mode is a full volume block level incremental replication feature. It replicates heterogeneous data from source partitions and volumes from UNIX and Windows clients to a NetApp C-mode destination filer as a single LUN with a single partition onto a destination qtree on a single destination volume. The source volumes can be carved out of disks that are locally attached to the client or from disks that are externally attached to the client from non-NetApp hardware arrays. It uses NetApp's OnCommand Unified Manager (OCUM) to provision the destination volumes to which data is replicated. Data is replicated as GPT LUN on Windows. On UNIX, LUN has the same format as the source volume LUN.

Running SnapProtect for Open Systems C-Mode (SPOS C-Mode) jobs from the replication workflow enables the use of a single destination NetApp volume as a fan-in destination for many clients under a single storage policy. It allows a group of clients to be controlled by a single job management context (providing a many-to-one control). This group defines the operations job unit which triggers the recovery point snapshots on the destination.

Using a consolidated destination automatically pull in any efficiencies that NetApp deduplication can achieve across the collection of the replicated disk images that are maintained by SPOS C-Mode.

The following illustration describes the process involved in SPOS C-Mode backup:

How SnapProtect for Open Systems C-Mode works

The SPOS C-Mode replication happens in the context of SnapProtect backup. To carry out the replication transfer, run or schedule the replication workflow from the storage policy to which all the clients that need to be protected are associated. Use OCUM to configure the storage policy copy to create a single destination volume that contains all the data for the source clients that are associated to the same storage policy.

The workflow, in turn, starts off individual SnapProtect backup jobs for each of the associated subclients. Each SnapProtect backup job for a subclient does the following:

  • Creates a software snapshot of the source data using the native snap engine such as VSS or LVM.
  • Mounts the destination qtree that corresponds to its source volume from the destination volume.
  • If the volume has never been protected before, then the SPOS C-Mode agent performs a baseline transfer, i.e., transfers all blocks for the volume to the destination filer
  • If the volume has been protected before, then the SPOS C-Mode agent calculates all blocks that have changed for the volume since the last backup, using the SHA-1 checksum mechanism and a checksum database to transfer only the changed blocks to the destination file server. For a given volume, all backups, except the first, are incremental.
  • Data is transferred using the NFS protocol wherein the client transferring the data acts as the NFS client and the filer as the NFS server.

When the SPOS C-Mode transfer of all associated subclients is completed, a single destination snapshot is taken on the destination volume and this snap is registered as the primary copy of data for that application each associated subclient against the primary snap copy. The software snapshot that was created at the start of the SnapProtect backup job is deleted once the SPOS C-Mode transfer for the source snapshot is successful.

The SnapProtect job type maybe full, differential, or incremental, but the SPOS C-Mode transfer is always incremental, once a baseline for a volume is established.

Processes Specific to SnapProtect for Open Systems C-Mode

Replication workflow – Coordinates the backup processes for all subclients of the replication workflow.

LREPListener – Runs on the source host and starts on-demand when the SPOS C-Mode backup runs. This is the service through which data gets transferred to the destination filer. LREPListener continues to run even after the backup is completed.

LREPCoordinator – Runs on the MediaAgent computer, that is associated to the storage policy where the SPOS C-Mode workflow job is triggered. It is responsible for creating the destination snap on the destination volume once the replication data for all subclients is successfully transferred.