Add ability to test pool recovery

README.md

@@ -96,3 +96,41 @@ sudo zdb -l /dev/sdX
 
 `wipefs --no-act` reports signatures without modifying the device. `zdb -l`
 should not find a readable ZFS label after a successful run.
+
+## Recovery Assessment
+
+`verify-zpool-recovery.sh` checks whether ZFS can find and rewind an exported
+or faulted pool. It cannot restore labels that have been completely overwritten
+by the eraser, so recovery after a successful erase is unlikely. Use it before
+erasing a device, or when ZFS still detects at least part of the pool metadata.
+
+List pools ZFS can discover without modifying anything:
+
+```bash
+sudo ./verify-zpool-recovery.sh
+```
+
+Check whether a specific pool can be recovered with a transaction rewind. This
+uses `zpool import -nF`, which is a dry run:
+
+```bash
+sudo ./verify-zpool-recovery.sh tank
+```
+
+If vdevs must be found in a non-default directory, supply it explicitly:
+
+```bash
+sudo ./verify-zpool-recovery.sh --directory /dev/disk/by-id tank
+```
+
+After reviewing the dry-run output, attempt the import with rewind recovery:
+
+```bash
+sudo ./verify-zpool-recovery.sh --apply tank
+```
+
+`--apply` runs `zpool import -N -F`: `-F` may discard the most recent
+transaction groups, and `-N` imports the pool without mounting datasets. The
+script requires the exact confirmation `RECOVER tank` before issuing that
+command. Inspect the result with `zpool status tank` before mounting datasets
+or performing any further changes.

verify-zpool-recovery.sh

@@ -0,0 +1,90 @@
+#!/usr/bin/env bash
+# Assess whether ZFS can rewind and import an exported or faulted pool.
+
+set -euo pipefail
+
+usage() {
+    cat <<'EOF'
+Usage: sudo ./verify-zpool-recovery.sh [--directory <path>] [--apply] [pool]
+
+Lists pools ZFS can discover, or checks whether a named pool can be recovered
+with a transaction rewind. The default is a dry run and changes nothing.
+
+Options:
+    -d, --directory <path>  Search a specific directory for vdev devices.
+    --apply                 Import the named pool with rewind recovery.
+    -h, --help              Show this help message.
+
+Without a pool name, the script only lists importable pools. --apply requires
+a pool name and imports it with datasets left unmounted.
+EOF
+}
+
+die() {
+    printf 'Error: %s\n' "$*" >&2
+    exit 1
+}
+
+search_directory=
+apply=false
+pool=
+
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        -d|--directory)
+            [[ $# -ge 2 ]] || die "$1 requires a path."
+            search_directory=$2
+            shift 2
+            ;;
+        --apply)
+            apply=true
+            shift
+            ;;
+        -h|--help)
+            usage
+            exit 0
+            ;;
+        -*)
+            die "unknown option '$1'."
+            ;;
+        *)
+            [[ -z $pool ]] || die 'specify at most one pool name or GUID.'
+            pool=$1
+            shift
+            ;;
+    esac
+done
+
+[[ $EUID -eq 0 ]] || die 'run as root (for example, with sudo).'
+command -v zpool >/dev/null 2>&1 || die "required command 'zpool' was not found."
+
+directory_args=()
+if [[ -n $search_directory ]]; then
+    [[ -d $search_directory ]] || die "'$search_directory' is not a directory."
+    directory_args=(-d "$search_directory")
+fi
+
+if [[ -z $pool ]]; then
+    [[ $apply == false ]] || die '--apply requires a pool name or GUID.'
+    printf 'Discovering importable pools. This does not modify any pool.\n\n'
+    zpool import "${directory_args[@]}"
+    exit 0
+fi
+
+if zpool list -H -o name "$pool" >/dev/null 2>&1; then
+    die "'$pool' is already imported; inspect it with 'zpool status $pool'."
+fi
+
+if [[ $apply == false ]]; then
+    printf 'Dry-run rewind recovery check for pool %s. No changes will be made.\n\n' "$pool"
+    zpool import -nF "${directory_args[@]}" "$pool"
+    exit 0
+fi
+
+printf '\nWARNING: this will attempt to rewind and import pool:\n  %s\n\n' "$pool"
+printf 'This can discard the most recent transaction groups. Datasets will remain unmounted.\n'
+read -r -p "Type exactly 'RECOVER $pool' to continue: " confirmation
+[[ $confirmation == "RECOVER $pool" ]] || die 'confirmation did not match; no changes were made.'
+
+zpool import -N -F "${directory_args[@]}" "$pool"
+printf "Pool '%s' was imported without mounting datasets. Inspect it with:\n  zpool status %s\n" "$pool" "$pool"