diff --git a/.github/actions/truenas-appliance-runner/action.yml b/.github/actions/truenas-appliance-runner/action.yml
index ec035a1..e533d1f 100644
--- a/.github/actions/truenas-appliance-runner/action.yml
+++ b/.github/actions/truenas-appliance-runner/action.yml
@@ -62,6 +62,13 @@ inputs:
   data-disk-gb:
     description: Size of each data disk.
     default: '10'
+  extra-disk-gb:
+    description: >-
+      More sparse disks after the data disks, one per size in GB, separated
+      by spaces: '32' adds one 32 GB disk, '12 12 15' three. For what ten
+      alike cannot give, such as a disk big enough to mirror the boot pool
+      onto. Not for an HA pair.
+    default: ''
   ssh:
     description: '`true` enables ssh for the admin, on TN_SSH.'
     default: 'false'
@@ -106,6 +113,7 @@ runs:
         APPLIANCE_VCPUS: ${{ inputs.vcpus }}
         APPLIANCE_DATA_DISKS: ${{ inputs.data-disk-count }}
         APPLIANCE_DATA_DISK_GB: ${{ inputs.data-disk-gb }}
+        APPLIANCE_EXTRA_DISK_GB: ${{ inputs.extra-disk-gb }}
         APPLIANCE_SSH: ${{ inputs.ssh }}
         APPLIANCE_DISK_INPUT: ${{ inputs.disk }}
         EXPORT_ENV: ${{ inputs.export-env }}
@@ -114,6 +122,12 @@ runs:
         set -euo pipefail
         lib="$GITHUB_ACTION_PATH"
         [ -n "$APPLIANCE_DISK_INPUT" ] && export APPLIANCE_DISK="$APPLIANCE_DISK_INPUT"
+        # ha.sh would ignore it, and a suite would then skip whatever
+        # wanted the disks without saying why.
+        if [ "$HA" = true ] && [ -n "$APPLIANCE_EXTRA_DISK_GB" ]; then
+          echo "::error::extra-disk-gb is for one appliance; an HA pair has only the data-disk-count disks its nodes share"
+          exit 1
+        fi
         export APPLIANCE_DIR="$RUNNER_TEMP/truenas-appliance"
         # The password is made here, so it is masked before anything can
         # print it.
diff --git a/.github/actions/truenas-appliance-runner/appliance.sh b/.github/actions/truenas-appliance-runner/appliance.sh
index 237d41f..c49e4cb 100755
--- a/.github/actions/truenas-appliance-runner/appliance.sh
+++ b/.github/actions/truenas-appliance-runner/appliance.sh
@@ -35,6 +35,8 @@
 #                         (default $RUNNER_TEMP/truenas-appliance)
 #   APPLIANCE_MEMORY_MB   6144       APPLIANCE_VCPUS        4
 #   APPLIANCE_DATA_DISKS  10         APPLIANCE_DATA_DISK_GB 10 (sparse)
+#   APPLIANCE_EXTRA_DISK_GB  more sparse disks after those, one per size in
+#                         GB, space-separated: "32", "12 12 15" (default none)
 #   APPLIANCE_HTTP_PORT   8080       APPLIANCE_HTTPS_PORT   8443
 #   APPLIANCE_SSH_PORT    2222       APPLIANCE_SSH          false
 #   APPLIANCE_BASELINE    fresh-install: the snapshot start takes; empty
@@ -97,12 +99,18 @@ start() {
     local disk="${APPLIANCE_DISK:-}"
     local memory="${APPLIANCE_MEMORY_MB:-6144}" vcpus="${APPLIANCE_VCPUS:-4}"
     local ndata="${APPLIANCE_DATA_DISKS:-10}" datagb="${APPLIANCE_DATA_DISK_GB:-10}"
+    local extragb=()
+    read -r -a extragb <<< "${APPLIANCE_EXTRA_DISK_GB:-}"
     local http="${APPLIANCE_HTTP_PORT:-8080}" https="${APPLIANCE_HTTPS_PORT:-8443}" sshp="${APPLIANCE_SSH_PORT:-2222}"
     local baseline="${APPLIANCE_BASELINE-fresh-install}"
     local password="${APPLIANCE_PASSWORD:-$(head -c 15 /dev/urandom | base64 | tr -d '/+=')}"
     local name="appliance-${GITHUB_RUN_ID:-local}-${GITHUB_RUN_ATTEMPT:-1}-${GITHUB_JOB:-job}"
 
     running && die "an appliance is running already ($DIR)"
+    local gb
+    for gb in "${extragb[@]}"; do
+        [[ "$gb" =~ ^[1-9][0-9]*$ ]] || die "APPLIANCE_EXTRA_DISK_GB: \"$gb\" is not a whole number of GB"
+    done
     needs qemu-system-x86_64 qemu-system-x86 qemu-img qemu-utils python3 python3
     ovmf
     local accel="${APPLIANCE_ACCEL:-kvm}" cpu=host
@@ -135,9 +143,23 @@ start() {
         drives+=(-drive "file=$DIR/data$i.qcow2,if=none,id=data$i,format=qcow2,discard=unmap"
                  -device "virtio-blk-pci,drive=data$i,serial=data$i")
     done
+    # After the data disks, so a suite that takes the first unused disks
+    # still gets data disks, all of one size.
+    local nextra=0
+    for gb in "${extragb[@]}"; do
+        nextra=$((nextra + 1))
+        qemu-img create -q -f qcow2 "$DIR/extra$nextra.qcow2" "${gb}G"
+        drives+=(-drive "file=$DIR/extra$nextra.qcow2,if=none,id=extra$nextra,format=qcow2,discard=unmap"
+                 -device "virtio-blk-pci,drive=extra$nextra,serial=extra$nextra")
+    done
+    local extrasaid=""
+    if [ "$nextra" -gt 0 ]; then
+        extrasaid=", and $nextra more of $(printf '%sG ' "${extragb[@]}")"
+        extrasaid="${extrasaid% }"
+    fi
 
     local booted t0
-    say "booting $disk as $name: ${memory} MB, $vcpus vCPUs, $ndata data disks of ${datagb}G"
+    say "booting $disk as $name: ${memory} MB, $vcpus vCPUs, $ndata data disks of ${datagb}G$extrasaid"
     t0=$(date +%s.%N)
     qemu-system-x86_64 -name "$name" -machine "q35,accel=$accel" -cpu "$cpu" -smp "$vcpus" -m "$memory" \
         -smbios "type=1,serial=$name" \
diff --git a/README.md b/README.md
index fb9b51a..e5cccd8 100644
--- a/README.md
+++ b/README.md
@@ -554,6 +554,7 @@ jobs:
 | `baseline` | `fresh-install` | Snapshot (`savevm`) taken once it is up; empty takes none |
 | `memory-mb`, `vcpus` | `6144`, `4` | The appliance's; the runner's flavor needs room for it and the job |
 | `data-disk-count`, `data-disk-gb` | `10`, `10` | Sparse qcow2 files |
+| `extra-disk-gb` | none | More sparse disks after the data disks, one per size in GB: `'32'`, `'12 12 15'`. Not for an HA pair |
 | `ssh` | `'false'` | `true` enables ssh for the admin, on `TN_SSH` |
 | `disk` | the attached one | Found by its serial, `virtio-truenas_appliance`, where the box keeps it; TrueNAS replaces it, so otherwise the one disk besides the root disk that holds a ZFS `boot-pool` |
 | `export-env` | `'true'` | Write `TN_*` to the job environment |