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OSDP C-Mode Overview

Open Systems Data Protection (OSDP) C-Mode is a full-volume block-level incremental replication feature. It replicates heterogeneous data from UNIX and Windows partitions and volumes to NetApp C-Mode destination filer. The replicated volume is a single LUN, with a single partition, on a destination qtree on a single destination volume.

Technical Details of the OSDP C-Mode Feature

The source volumes can be part of disks that are local or that are attached to the client. Or the source volumes can be from disks that are externally attached to the client from non-NetApp hardware arrays. OSDP C-Mode uses OnCommand Unified Manager (OCUM) to provision the destination volumes to which data is replicated. On Windows volumes, data is replicated as a GUID Partition Table (GPT) LUN. On UNIX volumes, the replicated LUN has the same format as the source LUN.

How OSDP C-Mode Feature Works

OSDP C-Mode replicates data by using a replication workflow instead of using backup operations. Using a workflow for replication provides many advantages, including the following:

  • The replication workflow defines the operations job unit that triggers the recovery point snapshots on the destination.
  • The replication workflow triggers and coordinates the backup jobs on all clients, using a single storage policy and creating a single destination NetApp volume.
  • The replication workflow controls all clients, providing many-to-one control.
  • You can easily achieve the efficiency of deduplication on all replicated disks, because all replicated disks are part of a single destination.

The replication workflow starts an IntelliSnap backup job for each subclient that is associated with the OSDP C-Mode storage policy. Each IntelliSnapbackup job does the following:

  • Creates a software snapshot of the source data using the native snap engine, such as Volume Shadow Service (VSS) or Logical Volume Manager (LVM).
  • Mounts the destination qtree that corresponds to the qtree in the source volume on the destination volume.
  • Transfers data using the NFS (Network File System) protocol. That is, the client transfers data to the destination filer as an NFS client, and the destination filer receives the data as an NFS server.

The type of backup that the replication workflow performs depends on whether the volume has been protected:

  • If the volume has never been protected, then the OSDP C-Mode agent performs a baseline transfer. That is, the OSDP C-Mode agent performs a full backup, which transfers all volume blocks to the destination filer.
  • If the volume has been protected, then the OSDP C-Mode agent first calculates the blocks on the volume that changed after the last backup. (To perform this calculation, the OSDP C-Mode agent uses the SHA-1 checksum mechanism and a checksum database. However, you can use optimized block-level replication, which is faster and more efficient.) Then, the OSDP C-Mode agent transfers only the changed blocks to the destination filer.

When the OSDP C-Mode agent transfers all snapshots of the subclients, a single destination snapshot is taken on the destination volume. The snapshot is the primary copy of data for that application each associated subclient against the primary snap copy. After the OSDP C-Mode agent successfully transfers a source snapshot, the software snapshot that was created at the start of the IntelliSnap backup job is deleted.

Although the OSDP C-Mode agent always performs incremental backups after performing an initial full backup, the IntelliSnap backup job can be full, differential, or incremental.

The following figure shows the process that is involved in an OSDP C-Mode backup:

Last modified: 3/1/2018 4:46:08 PM