{
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-14",
  "slug": "zfs-separate-log",
  "term": "ZFS separate log",
  "aliases": [
    "SLOG",
    "separate intent log device"
  ],
  "definition": "A ZFS separate log is dedicated pool log-device storage used for intent-log blocks instead of their default allocation in the main pool.",
  "note": "A SLOG is optional, not the ZIL itself and not a general write cache or independent backup. Log devices may be mirrored, but RAID-Z log vdevs are not supported. [pool-man] logbias=throughput bypasses configured log devices while retaining synchronous semantics; sync=disabled instead ignores application synchronous requests. [props-man] Data protected by an indirect log record need not be copied into the SLOG. [write-source]",
  "related": [
    "zfs-intent-log",
    "zfs-transaction-group",
    "write-back-cache",
    "power-loss-protection",
    "fsync"
  ],
  "citations": [
    {
      "id": "pool-man",
      "title": "OpenZFS 2.3: zpoolconcepts(7), Intent Log and Cache Devices",
      "url": "https://openzfs.github.io/openzfs-docs/man/v2.3/7/zpoolconcepts.7.html",
      "accessed": "2026-10-14"
    },
    {
      "id": "props-man",
      "title": "OpenZFS 2.3: zfsprops(7), sync and logbias",
      "url": "https://openzfs.github.io/openzfs-docs/man/v2.3/7/zfsprops.7.html",
      "accessed": "2026-10-14"
    },
    {
      "id": "write-source",
      "title": "OpenZFS 2.3.4: zfs_log.c, zfs_log_write selection of write state",
      "url": "https://github.com/openzfs/zfs/blob/zfs-2.3.4/module/zfs/zfs_log.c",
      "accessed": "2026-10-14"
    }
  ]
}