diff --git a/modules/hardware.nix b/modules/hardware.nix
index 907729c..32ac735 100644
--- a/modules/hardware.nix
+++ b/modules/hardware.nix
@@ -5,6 +5,20 @@
   service_configs,
   ...
 }:
+let
+  hddTuneIosched = pkgs.writeShellScript "hdd-tune-iosched" ''
+    # Called by udev with the partition kernel name (e.g. sdb1).
+    # Derives the parent disk and applies mq-deadline iosched params.
+    parent=''${1%%[0-9]*}
+    dev="/sys/block/$parent"
+    [ -d "$dev/queue/iosched" ] || exit 0
+    echo 15000 > "$dev/queue/iosched/read_expire"
+    echo 15000 > "$dev/queue/iosched/write_expire"
+    echo 128 > "$dev/queue/iosched/fifo_batch"
+    echo 16 > "$dev/queue/iosched/writes_starved"
+    echo 4096 > "$dev/queue/max_sectors_kb" 2>/dev/null || true
+  '';
+in
 {
   boot.initrd.availableKernelModules = [
     "xhci_pci"
@@ -30,48 +44,13 @@
   # fifo_batch=128 keeps sweeps long; writes_starved=16 heavily favors reads.
   # 4 MiB readahead matches libtorrent piece extent affinity for sequential prefetch.
   #
-  # This runs as a systemd oneshot rather than udev rules because the NixOS ZFS module
-  # hardcodes a udev rule that forces scheduler="none" on all ZFS member partitions'
-  # parent disks, overriding any scheduler set via udev on the disk event.
-  systemd.services.hdd-io-tuning = {
-    description = "HDD I/O scheduler and queue tuning";
-    after = [
-      "zfs-import.target"
-      "systemd-udev-settle.service"
-    ];
-    wantedBy = [ "multi-user.target" ];
-    serviceConfig = {
-      Type = "oneshot";
-      RemainAfterExit = true;
-    };
-    path = with pkgs; [
-      coreutils
-      gawk
-      zfs
-    ];
-    script = ''
-      # Only tune disks in the hdds pool — not all rotational disks.
-      # zpool status gives by-id device names; we resolve to /sys/block/<name>.
-      zpool status hdds | awk '/^\t/ && $1 ~ /^(ata-|nvme-|scsi-)/ {print $1}' | while read -r id; do
-        link="/dev/disk/by-id/$id"
-        [ -L "$link" ] || continue
-        name=$(basename "$(readlink -f "$link")")
-        dev="/sys/block/$name"
-        [ -d "$dev" ] || continue
-
-        echo mq-deadline > "$dev/queue/scheduler"
-        echo 4096 > "$dev/queue/read_ahead_kb"
-        echo 512 > "$dev/queue/nr_requests"
-
-        echo 15000 > "$dev/queue/iosched/read_expire"
-        echo 15000 > "$dev/queue/iosched/write_expire"
-        echo 128 > "$dev/queue/iosched/fifo_batch"
-        echo 16 > "$dev/queue/iosched/writes_starved"
-
-        echo 4096 > "$dev/queue/max_sectors_kb" 2>/dev/null || true
-
-        echo "Tuned $id -> $name: mq-deadline, 4M readahead, 15s deadlines"
-      done
-    '';
-  };
+  # The NixOS ZFS module hardcodes a udev rule that forces scheduler="none" on all
+  # ZFS member partitions' parent disks (on both add AND change events). We counter
+  # it with lib.mkAfter so our rule appears after theirs in 99-local.rules — our
+  # rule matches the same partition events and sets mq-deadline back, then a RUN
+  # script applies the iosched params. Only targets rotational, non-removable disks
+  # (i.e. HDDs, not SSDs or USB).
+  services.udev.extraRules = lib.mkAfter ''
+    ACTION=="add|change", KERNEL=="sd[a-z]*[0-9]*", ENV{ID_FS_TYPE}=="zfs_member", ATTR{../queue/rotational}=="1", ATTR{../removable}=="0", ATTR{../queue/scheduler}="mq-deadline", ATTR{../queue/read_ahead_kb}="4096", ATTR{../queue/nr_requests}="512", RUN+="${hddTuneIosched} %k"
+  '';
 }