diff --git a/docs/contrib/dgx-spark.md b/docs/contrib/dgx-spark.md
index 6002046d1..b7d637cb7 100644
--- a/docs/contrib/dgx-spark.md
+++ b/docs/contrib/dgx-spark.md
@@ -140,6 +140,10 @@ BLOOMERY_BOX_LOCAL=1 BLOOMERY_BOX_ENV='BLOOMERY_TIER=fixture BLOOMERY_GATE_BOUND
   reference set's identity is the first shard's full path (`AGENTS.md`; a set's `# model` line,
   `crates/refset/src/fixture.rs:19-20`). `/models/fixtures` stays the one legal root, so on a Spark it is a symlink
   (answer 2).
+- **Container drive counters.** The depth, nvtier-read and engram-rate runners resolve a model's mount through
+  `tools/ref/drive-read.sh`: `findmnt --nofsroot` removes a bind mount's bracketed root, then `lsblk` resolves the
+  whole-disk parent or kernel name. The container must expose readable `/sys/block/<disk>/stat` counters.
+  A mount or counter that cannot be read is a named exit 2 before timing, not a guessed device or a weaker witness.
 - **Card names.** A Spark's card is named neither 3090 nor A6000, and local mode takes the one local card without a name
   match. `--place gate` plans the 3090's bytes on the smallest visible card with the room for them, the GB10 here, and local mode refuses the
   two-card recipes (rc 64) ([#13](https://github.com/midagedev/bloomery/issues/13#issuecomment-6124298082)). Which
diff --git a/tools/ref/card-tests/run.sh b/tools/ref/card-tests/run.sh
index 2c96cb32a..629d302f1 100755
--- a/tools/ref/card-tests/run.sh
+++ b/tools/ref/card-tests/run.sh
@@ -97,6 +97,46 @@ has() {
   if grep -Eq -- "$2" "$tmp/out"; then pass "$1"; else fail "$1" "no line matches /$2/" "$tmp/out"; fi
 }
 
+# The drive reader against a bind-root source, a whole-disk alias and absent counters. Only the
+# mount/block-device commands and /sys readability stand in; no disk or Linux /sys is needed.
+drive_case() (
+  mode=$1
+  source "$ROOT/tools/ref/drive-read.sh"
+  findmnt() {
+    [ "$mode" != unmounted ] || return 1
+    case "$mode" in
+      alias) echo /dev/disk/by-id/test-alias ;;
+      fallback) echo /dev/testdisk ;;
+      *)
+        case " $* " in
+          *" --nofsroot "*) echo /dev/testp1 ;;
+          *) echo '/dev/testp1[/models]' ;;
+        esac
+        ;;
+    esac
+  }
+  lsblk() {
+    case "$3:$4" in
+      PKNAME:/dev/testp1) echo testdisk ;;
+      KNAME:/dev/disk/by-id/test-alias) echo testdisk ;;
+      *) return 1 ;;
+    esac
+  }
+  function [ {
+    if builtin [ "${1:-}" = -r ] && [[ "${2:-}" = /sys/block/*/stat ]]; then
+      builtin [ "$mode" != nocounters ] && builtin [ "$2" = /sys/block/testdisk/stat ]
+    else
+      builtin [ "$@"
+    fi
+  }
+  drive_dev '/models with space/model.gguf'
+)
+run 'drive: a bind root resolves to the whole disk' 0 '^testdisk$' drive_case bind
+run 'drive: a whole-disk alias resolves through KNAME' 0 '^testdisk$' drive_case alias
+run 'drive: a canonical disk with no lsblk row retains its counters' 0 '^testdisk$' drive_case fallback
+run 'drive: absent counters are a named refusal' 2 'no counters at /sys/block/testdisk/stat' drive_case nocounters
+run 'drive: an unreadable mount is a named refusal' 2 'findmnt cannot name the mount of /models with space' drive_case unmounted
+
 # card <fixture> <rc> <pattern> [args…]: card.py check on a fixture of this directory.
 card() {
   local f=$1 want=$2 pat=$3
diff --git a/tools/ref/drive-read.sh b/tools/ref/drive-read.sh
index 98eaf534a..95eefe0e9 100644
--- a/tools/ref/drive-read.sh
+++ b/tools/ref/drive-read.sh
@@ -1,17 +1,24 @@
 # shellcheck shell=bash
 # The drive a model file is read from, and what the drive was asked to read (nvtier-read.sh,
-# depth-qwen3moe.sh): the device is read from the file's mount, never guessed, and its counters are the
+# depth-qwen3moe.sh, engram-rate.sh): the device is read from the file's mount, never guessed, and its counters are the
 # kernel's own (/sys/block/<dev>/stat, field 3: sectors read, 512 B each — the number /proc/diskstats
 # prints as its sixth column). Sourced; it defines functions and runs nothing.
 
+# drive_source <file>: the mount's device, without a bind mount's bracketed filesystem root.
+drive_source() {
+  local dir
+  dir=$(dirname "$1")
+  findmnt --nofsroot -n -o SOURCE --target "$dir" || { echo "drive-read.sh: findmnt cannot name the mount of $dir" >&2; return 2; }
+}
+
 # drive_dev <file>: the whole-disk device of the mount <file>'s directory sits on, on stdout; rc 2 with the
 # reason on stderr when the mount or its counters cannot be read (a drive whose counters cannot be read is
 # no instrument).
 drive_dev() {
-  local dir src dev
-  dir=$(dirname "$1")
-  src=$(findmnt -n -o SOURCE --target "$dir") || { echo "drive-read.sh: findmnt cannot name the mount of $dir" >&2; return 2; }
+  local src dev
+  src=$(drive_source "$1") || return 2
   dev=$(lsblk -n -o PKNAME "$src" 2> /dev/null | head -n1 || true)
+  [ -n "$dev" ] || dev=$(lsblk -n -o KNAME "$src" 2> /dev/null | head -n1 || true)
   [ -n "$dev" ] || dev=$(basename "$src")
   [ -r "/sys/block/$dev/stat" ] || { echo "drive-read.sh: no counters at /sys/block/$dev/stat (mount source $src, device $dev)" >&2; return 2; }
   echo "$dev"
diff --git a/tools/ref/engram-rate.sh b/tools/ref/engram-rate.sh
index 5c6d93331..222f8bc3d 100755
--- a/tools/ref/engram-rate.sh
+++ b/tools/ref/engram-rate.sh
@@ -17,18 +17,17 @@ export BLOOMERY_DATA
 # The lease and the witness fields.
 # shellcheck source=tools/ref/lease.sh
 source "${BASH_SOURCE[0]%/*}/lease.sh"
+# shellcheck source=tools/ref/drive-read.sh
+source "${BASH_SOURCE[0]%/*}/drive-read.sh"
 
 BIN=${BLOOMERY_ENGRAM_BIN:-target/release/engram-rate}
 [ -x "$BIN" ] || { echo "no engram-rate at $BIN — run: just build-engram" >&2; exit 2; }
 
 # The V4.1 file set: the deepseek41 profile's choice, exported by tools/box.sh.
 DIR=${BLOOMERY_V41_DIR:?BLOOMERY_V41_DIR unset — run through tools/box.sh, which exports it from the deepseek41 profile}
-# 테이블이 어느 블록 디바이스에 있는지는 추측하지 않는다 — 마운트에서 읽는다.
-SRC=$(findmnt -n -o SOURCE --target "$DIR")
-# `|| true` 안에서 받는다: set -e 아래에서는 대입 안의 파이프라인이 실패하면 그 줄에서 죽어,
-# 다음 줄의 폴백이 영영 안 돈다. 발견이 실패해도 러너는 증인만 약해진 채 계속 가야 한다.
-DEV=$(lsblk -n -o PKNAME "$SRC" 2>/dev/null | head -n1 || true)
-[ -n "$DEV" ] || DEV=$(basename "$SRC")
+# The shared reader resolves bind roots and refuses a drive with no readable counters.
+SRC=$(drive_source "$DIR/.") || exit 2
+DEV=$(drive_dev "$DIR/.") || exit 2
 STAT=/sys/block/$DEV/stat
 
 WITNESS=(head table loadavg pressure-io blockstat meminfo lock-holder model)
diff --git a/tools/ref/nvtier-read.sh b/tools/ref/nvtier-read.sh
index 30904d016..918e70cdb 100755
--- a/tools/ref/nvtier-read.sh
+++ b/tools/ref/nvtier-read.sh
@@ -218,7 +218,7 @@ echo "[binary] $BIN sha256=$BIN_SHA mtime=$BIN_MTIME (newer than every file in i
 DIR=$(dirname "$MODEL")
 DEV=$(drive_dev "$MODEL") || exit 2
 # The witness's table and blockstat fields read the mount source and the device's counters.
-SRC=$(findmnt -n -o SOURCE --target "$DIR")
+SRC=$(drive_source "$MODEL") || exit 2
 STAT=/sys/block/$DEV/stat
 
 WITNESS=(head loadavg pressure-cpu pressure-io table blockstat meminfo pgmajfault cpu cpu-mhz-range lock-holder binary model)