{
  "slug": "virtual-guard",
  "term": "Virtual Guard",
  "aliases": [
    "Vguard"
  ],
  "definition": "Virtual Guard is a research SMR translation layer that caches a neighboring track so the target track can be updated in place.",
  "note": "Before overwriting a track, Virtual Guard preserves its next track in the shingling direction in persistent cache, unless that neighbor is already protected or the target ends a band. Repeated writes can then reuse the same protection. [vguard]\n\nCleaning restores cached tracks to their home bands. It is triggered by free-track or log-distance thresholds, not idle time alone: cleaning too early would remove protection useful for subsequent writes. [vguard]\n\nThe evaluation used a Python disk simulator, unscaled trace addresses, queue depth one and no inter-request delay, with volatile write cache disabled. The tested workloads with spatial locality avoided cleaning; broad synthetic random writes still triggered it. [vguard]",
  "limitations": [
    {
      "text": "Repeated in-place overwrites remain subject to upstream track interference, and hardware validation was left for future work.",
      "citationIds": [
        "vguard"
      ]
    }
  ],
  "related": [
    "shingle-translation-layer",
    "garbage-collection-smr",
    "smart-smr-translation"
  ],
  "provenance": [
    "Full HotStorage 2017 paper reviewed. Performance results are simulations, not measurements of a shipping Vguard drive or a Hesela replication.",
    "Sections 2.1-2.3 define protected neighbors, map persistence and cleaning. Sections 3-4 bound trace replay and future hardware validation."
  ],
  "status": "research",
  "advantages": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "vguard",
      "title": "Shafaei and Desnoyers. Virtual Guard: A Track-Based Translation Layer for Shingled Disks. HotStorage 2017, sections 2-4",
      "url": "https://www.usenix.org/system/files/conference/hotstorage17/hotstorage17-paper-shafaei.pdf",
      "accessed": "2026-11-14"
    }
  ],
  "updated": "2026-11-14"
}