{
  config,
  lib,
  pkgs,
  service_configs,
  ...
}:
{
  boot.initrd.availableKernelModules = [
    "xhci_pci"
    "ahci"
    "usb_storage"
    "usbhid"
    "sd_mod"
  ];
  boot.initrd.kernelModules = [ "dm-snapshot" ];
  boot.kernelModules = [ "kvm-amd" ];
  boot.extraModulePackages = [ ];

  swapDevices = [ ];

  hardware.cpu.amd.updateMicrocode = true;
  hardware.enableRedistributableFirmware = true;

  # HDD I/O tuning for torrent seeding workload (high-concurrency random reads).
  #
  # mq-deadline sorts requests into elevator sweeps, reducing seek distance.
  # Aggressive deadlines (15s) let the scheduler accumulate more ops before dispatching,
  # maximizing coalescence — latency is irrelevant since torrent peers tolerate 30-60s.
  # 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
    '';
  };
}