{
  "slug": "dev-loss-tmo",
  "term": "dev_loss_tmo (transport device loss)",
  "aliases": [
    "Device-loss timeout"
  ],
  "definition": "In Linux's Fibre Channel transport, dev_loss_tmo is the interval in seconds for retaining a missing remote target before device-removal processing.",
  "note": "Linux v6.12 separates device-loss work from fail-fast work; target removal affects the operating system's devices, not erasure of the stored data. It does not establish whether an earlier write executed. [linux-fc-timers]\n\nThe reviewed multipath manual applies this setting to FC and SAS, not every transport. With positive fast_io_fail_tmo and finite no_path_retry N, multipathd keeps dev_loss_tmo larger than N times polling_interval. Premature removal while I/O remains queued can deadlock. Inspect the effective settings together. [multipath-man]\n\nThese FC path-loss timers do not trigger if the remote port is never reported lost, even when SCSI commands hang. The manual discusses eh_deadline for that different condition and warns that its HBA reset affects all target paths on the adapter. [multipath-man]",
  "related": [
    "fast-io-fail-tmo",
    "no-path-retry",
    "multipath-io",
    "io-timeout",
    "fibre-channel",
    "sas"
  ],
  "citations": [
    {
      "id": "linux-fc-timers",
      "title": "Linux v6.12: FC transport loss, fail-fast and target-removal work.",
      "url": "https://raw.githubusercontent.com/torvalds/linux/v6.12/drivers/scsi/scsi_transport_fc.c",
      "accessed": "2026-10-23"
    },
    {
      "id": "multipath-man",
      "title": "multipath-tools: multipath.conf(5), no_path_retry and FC timeout options; pinned commit d53932bdbee02f440518ea384e63d7c4d3f66685.",
      "url": "https://github.com/opensvc/multipath-tools/blob/d53932bdbee02f440518ea384e63d7c4d3f66685/multipath/multipath.conf.5.in",
      "accessed": "2026-10-23"
    },
    {
      "id": "hesela-timeouts",
      "title": "Storage timeouts: an expired timer is not a cancelled write",
      "url": "https://hesela.com/analyses/storage-timeouts-uncertain-completion/",
      "accessed": "2026-10-23"
    }
  ],
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-24",
  "provenance": [
    "The FC definition follows Linux v6.12. FC/SAS applicability and queue-budget coordination follow the pinned multipath-tools manual. Non-erasure and uncertain-write conclusions are editorial interpretation, not measured outcomes."
  ]
}