qbt: delete incomplete subvolume + tweaks

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

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"
@@ -55,12 +53,12 @@
 
     serverConfig.BitTorrent = {
       Session = {
-        MaxConnectionsPerTorrent = 50;
-        MaxUploadsPerTorrent = 10;
+        MaxConnectionsPerTorrent = 100;
+        MaxUploadsPerTorrent = 15;
         MaxConnections = -1;
         MaxUploads = -1;
 
-        MaxActiveCheckingTorrents = 5;
+        MaxActiveCheckingTorrents = 2; # reduce disk pressure from concurrent hash checks
 
         # queueing
         QueueingSystemEnabled = true;
@@ -91,7 +89,7 @@
         inherit (config.services.qbittorrent.serverConfig.Preferences.Downloads) TempPath;
         TempPathEnabled = true;
 
-        ConnectionSpeed = 200;
+        ConnectionSpeed = 30;
 
         # Automatic Torrent Management: use category save paths for new torrents
         DisableAutoTMMByDefault = false;
@@ -102,6 +100,22 @@
         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 = {