qbt: tune

configuration.nix

@@ -157,6 +157,9 @@
 
       # Higher backlog for the large number of concurrent torrent connections
       "net.core.netdev_max_backlog" = 5000;
+      # Faster cleanup of dead connections from torrent peer churn
+      "net.ipv4.tcp_fin_timeout" = 15; # default 60
+      "net.ipv4.tcp_tw_reuse" = 1;
 
       # Minecraft server optimizations
       # Disable autogroup for better scheduling of game server threads

modules/zfs.nix

@@ -27,13 +27,17 @@ in
 
   boot.kernelParams =
     let
-      gb = 20;
+      gb = 32;
       mb = gb * 1000;
       kb = mb * 1000;
       b = kb * 1000;
     in
     [
       "zfs.zfs_arc_max=${builtins.toString b}"
+      "zfs.zfs_txg_timeout=30" # longer TXG open time = larger sequential writes = better HDD throughput
+      "zfs.zfs_dirty_data_max=8589934592" # 8GB dirty data buffer (default 4GB) for USB HDD write smoothing
+      "zfs.zfs_delay_min_dirty_percent=80" # delay write throttling until 80% dirty (default 60%)
+      "zfs.zfs_vdev_async_write_max_active=30" # more concurrent async writes to vdevs (default 10)
     ];
 
   boot.supportedFilesystems = [ "zfs" ];

services/qbittorrent.nix

@@ -10,8 +10,6 @@
   imports = [
     (lib.serviceMountWithZpool "qbittorrent" service_configs.zpool_hdds [
       service_configs.torrents_path
-      config.services.qbittorrent.serverConfig.Preferences.Downloads.TempPath
-
     ])
     (lib.serviceMountWithZpool "qbittorrent" service_configs.zpool_ssds [
       "${config.services.qbittorrent.profileDir}/qBittorrent"
@@ -55,22 +53,22 @@
 
     serverConfig.BitTorrent = {
       Session = {
-        MaxConnectionsPerTorrent = 50;
+        MaxConnectionsPerTorrent = 100;
-        MaxUploadsPerTorrent = 10;
+        MaxUploadsPerTorrent = 15;
         MaxConnections = -1;
         MaxUploads = -1;
 
-        MaxActiveCheckingTorrents = 5;
+        MaxActiveCheckingTorrents = 2; # reduce disk pressure from concurrent hash checks
 
         # queueing
         QueueingSystemEnabled = true;
-        MaxActiveDownloads = 5; # keep focused: fewer torrents, each gets more bandwidth
+        MaxActiveDownloads = 15;
         MaxActiveUploads = -1;
         MaxActiveTorrents = -1;
         IgnoreSlowTorrentsForQueueing = true;
 
         GlobalUPSpeedLimit = 0;
-        GlobalDLSpeedLimit = 0;
+        GlobalDLSpeedLimit = 10000;
 
         # Alternate speed limits for when Jellyfin is streaming
         AlternativeGlobalUPSpeedLimit = 500; # 500 KB/s when throttled
@@ -91,7 +89,10 @@
         inherit (config.services.qbittorrent.serverConfig.Preferences.Downloads) TempPath;
         TempPathEnabled = true;
 
-        ConnectionSpeed = 200;
+        ConnectionSpeed = 100;
+
+        SaveResumeDataInterval = 300; # save resume data every 5 min (default 60s)
+        ResumeDataStorageType = "SQLite"; # SQLite is more efficient than legacy per-file .fastresume storage
 
         # Automatic Torrent Management: use category save paths for new torrents
         DisableAutoTMMByDefault = false;
@@ -102,6 +103,22 @@
         PieceExtentAffinity = true;
         SuggestMode = true;
         CoalesceReadWrite = true;
+
+        # max_queued_disk_bytes: the max bytes waiting in the disk I/O queue.
+        # When this limit is reached, peer connections stop reading from their
+        # sockets until the disk thread catches up -- causing the spike-then-zero
+        # pattern. Default is 1MB; high_performance_seed() uses 7MB.
+        # 64MB is above the preset but justified for slow raidz1 HDD random writes
+        # where ZFS txg commits cause periodic I/O stalls.
+        DiskQueueSize = 67108864; # 64MB
+
+        # === Network buffer tuning (from libtorrent high_performance_seed preset) ===
+        # "always stuff at least 1 MiB down each peer pipe, to quickly ramp up send rates"
+        SendBufferLowWatermark = 1024; # 1MB (KiB) -- matches high_performance_seed
+        # "of 500 ms, and a send rate of 4 MB/s, the upper limit should be 2 MB"
+        SendBufferWatermark = 3072; # 3MB (KiB) -- matches high_performance_seed
+        # "put 1.5 seconds worth of data in the send buffer"
+        SendBufferWatermarkFactor = 150; # percent -- matches high_performance_seed
       };
 
       Network = {
@@ -109,6 +126,8 @@
         # port forwarding
         PortForwardingEnabled = false;
       };
+
+      Session.UseUPnP = false;
     };
   };