Data Domain: How to resync Mtree replication

Summary: This article describes the procedure for performing a replication resynchronization (resync) on systems configured for MTree replication. The MTree resync workflow differs from directory or collection-based replication, so customers using MTree replication must follow this documented procedure. ...

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Symptoms

These steps apply to systems configured with basic one‑way replication (source → destination).
However, environments may include more complex configurations such as:

  • Bidirectional replication
  • Chained replication across multiple systems

When an MTree replication context is broken, the partner system must also have the matching context broken.

 
⚠️Warning: Before proceeding, understand the  differences between replication Resync and Initialization.

Cause

An MTree resync may be required for several reasons, including:

  • Cleaning not recovering disk space.
  • MTree replication lag exceeding retention requirements.
  • Replication panic associated with Fastcopy
  • AutoSupport alert: "Cannot recover from NVRAM: Recently written data may be lost."

Resolution

Important Notes

  • ⚠️Note: Do not disable unrelated replication contexts. These recover automatically when the filesystem is re‑enabled.
  • ⚠️Note: If the intention is to perform an initialization instead of a resync, delete the replicated MTree on the destination or rename the destination path after breaking the context.

Option 1: Resync using System Manager (Web-UI) - *Recommended

*Recommended, as it simplifies the procedure, is more efficient and avoids typos due to manual path entry.

  1. Break the existing replication context
    1. Open Enterprise Manager for the source system.
    2. Select Replication.
    3. Choose the replication context to break.
    4. Click Delete Pair.
    5. Confirm by clicking OK.
      • This removes the replication context from both systems.
  2. Start the resync
    1. In the same Replication tab, click More → Start Resync.
    2. Select MTree Replication as the replication type.
    3. Select the source and destination systems.
    4. Specify the MTree path on both systems.
    5. Click OK to begin the resync.
      • Resync duration varies from hours to days depending on system size and load.

Option 2: Resync using Command-Line (SSH/DD-CLI)

  1. Save the current replication configuration
    1. Run on both source and destination:
      • replication show config
        • Copy the output into a text editor for reference when rebuilding contexts.
  2. Break replication on the source system
    • Break a single context:
      • replication break rctx://<context-number> 
    • Break all contexts (only when required):
      • replication break context all
  3. Break related contexts on the destination system
    1. If the destination has only one partner, repeat the same steps as the source.
    2. If the destination has multiple replication partners, break only the shared contexts:
      • replication break rctx://<context-number>
  4. Re-create the replication contexts
    1. Using the saved configuration, re-create the MTree contexts on both systems:
  5. Start the resync (source system only)
    • replication resync rctx://<context-number>
    • Note: The context number may differ from the original if lower numbers were available.
  6. Monitor resync progress
    • replication watch rctx://<context-number>

Additional Information

The iostat command provides a broad system-level view. To avoid text wrapping and distorted output, maximize the display window when running this command.
If the source MTree or directory contains no data, the resync may complete too quickly to appear in monitoring output. Likewise, when no data is being written to the source, throughput values may be very low or may not appear at all.

Affected Products

Data Domain

Products

Data Domain
Article Properties
Article Number: 000035776
Article Type: Solution
Last Modified: 10 Feb 2026
Version:  4
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