Review TrueNAS hot-spare promotion before replacing a failed disk

Bottom line: Check whether the spare has already entered the data VDEV before planning the next disk action. Treat promotion of that active spare and restoration of the spare reserve as separate steps with separately checked device identities.

Source fact: what the authority says

The TrueNAS replacement guide says an available hot spare is automatically inserted into a data VDEV when an active drive fails, followed by a resilver. Its hot-spare procedure takes the failed disk offline, detaches that failed disk to promote the spare, then recreates the spare VDEV. The guide warns that using its ordinary replacement branch after a spare has entered the pool causes two resilvers and recommends promotion followed by recreating the reserve instead. A replacement disk must have at least the failed disk’s capacity, and the replacement process wipes its data.

What the source does not establish

These are the versioned TrueNAS procedures, not a diagnosis of the present pool or a compatibility statement for a drive. DSE leaves the actual hardware choice and any unsafe or unclear device state to the responsible storage owner and applicable manufacturer guidance.

Applicability questions

• Which physical disk failed, and what evidence maps that identity to the displayed VDEV member?
• Is a spare already active, and what reconstruction activity remains in progress?
• Which documented branch matches that observed state?
• What approved disk will restore the spare reserve, and is any existing data on it authorized for destruction?

DSE recommendation: controlled next steps

The following steps are DSE recommendations based on the cited source.

DSE recommends a before-action pool diagram showing the failed device, active replacement or spare, and remaining reserve. Have a second person check the physical-to-logical device mapping before removal. Write the selected branch beside the diagram so an operator does not begin the no-spare procedure merely because that is the first replacement sequence in the guide.

For a proposed case with an already activated spare, walk through promotion and recreation of the reserve as two different decisions. Identify which failed member would be detached and which new disk would become the spare. Keep the new disk’s identity, capacity and disposition of any existing contents explicit. Pause if the displayed state differs from the reviewed diagram.

Plan the service observation around the actual reconstruction state and the owner’s workload constraints. Keep any force option outside the ordinary plan until its purpose and destructive consequence have been separately reviewed. Do not close the incident on a completed physical swap alone; require the resulting member and reserve assignments to be reconciled with the intended pool design.

Have the final diagram show the promoted data member and newly assigned reserve as distinct identities. Require the reviewer to locate both in the actual status evidence. A familiar enclosure slot or reused disk description should not replace that identity check.

Verification and evidence

Proposed verification: rehearse the selected branch only on a disposable pool or under an appropriately approved storage procedure. Record the initial active-spare state, exact targeted device and resulting member assignment. Observe reconstruction through its actual completion and preserve the reported health information rather than assuming a predetermined duration.

Check the recreated spare VDEV separately and compare all final identities with the diagram. Have the storage owner review remaining errors, workload observations and reserve capacity before accepting the result. Retain before-and-after pool records and the second-person device check. Escalate an unexplained state instead of repeating a destructive action to obtain the expected screen.

Official references

• TrueNAS — Replacing Disks — official product documentation; confirm the installed release and configuration.

Source review completed October 28, 2026. Recheck the official documentation and deployment-specific applicability before a production change.