Snapshot, Microsoft VSS, and XAgent – White Paper

This article summarizes snapshot operations, Microsoft VSS, and the XAgent desktop application. It explains copy-on-write snapshots (management, rollback, writable snapshots), details VSS components and workflow, and describes integration via QSAN’s VSS hardware provider to ensure consistent, hardware-based snapshots in Windows environments.

Download: Snapshot, Microsoft VSS, and XAgent

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Key Sections:

  • Introduction: scope and purpose.
  • What is XAgent: desktop app for installing, uninstalling, and updating modules; includes Snapshot Agent to trigger the hardware provider and improve snapshot consistency.
  • What is Microsoft VSS: Windows technology for consistent backups/snapshots while data is in use; example scenarios (backup solutions, system restore, file recovery).
  • Theory of Operations:
    • Managing Snapshots: point-in-time protection supporting RPO/RTO goals; ransomware/accidental change mitigation.
    • Theory of Snapshots: copy-on-write mechanism; snapshot rollback; writable snapshots (independent, modifiable copies).
    • Disadvantages of Built-in Snapshot: host caching can cause incomplete data without a host agent.
  • Microsoft VSS Operations: roles of VSS Service, Requesters, Writers, and Providers; high-level workflow.
  • Integrated with Microsoft VSS: QSAN VSS hardware provider creates consistent, hardware-based snapshots coordinated by VSS.
  • Conclusion: use a host snapshot agent to ensure consistency; hardware-based snapshots enable reliable recovery points.
  • Appendix:
    • Apply To: XAgent 1.0.0+; QSM firmware 4.0.3+.
    • Reference: XAgent Software Manual; QSM 4 Software Manual.

Critical Notes:

  • CAUTION: Using only the storage built-in snapshot may result in incomplete data due to host caching; use the host snapshot agent for consistency.
  • TIP: Reserve about 20% (or more) of pool capacity for snapshot space.
  • INFORMATION: Performance data in the document were obtained in controlled environments and may vary.

JetStor Support

For assistance with snapshots and VSS on JetStor deployments:
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