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zfs-separate-log · shipping · also SLOG, separate intent log device

ZFS separate log

A ZFS separate log is dedicated pool log-device storage used for intent-log blocks instead of their default allocation in the main pool.

Related Observatory article: ZFS separate log on hesela.com

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. [1] logbias=throughput bypasses configured log devices while retaining synchronous semantics; sync=disabled instead ignores application synchronous requests. [2] Data protected by an indirect log record need not be copied into the SLOG. [3]

Relations

related
zfs-intent-log, zfs-transaction-group, write-back-cache, power-loss-protection, fsync

Citations

  1. OpenZFS 2.3: zpoolconcepts(7), Intent Log and Cache Devices (accessed 2026-10-14)
  2. OpenZFS 2.3: zfsprops(7), sync and logbias (accessed 2026-10-14)
  3. OpenZFS 2.3.4: zfs_log.c, zfs_log_write selection of write state (accessed 2026-10-14)

JSON: /data/terms/zfs-separate-log.json