From 57080293bb1c4ff5ae9316451e4bcd383d64ab9b Mon Sep 17 00:00:00 2001
From: Simon Gardling <titaniumtown@proton.me>
Date: Mon, 2 Mar 2026 23:33:15 -0500
Subject: [PATCH] zfs: tuning

---
 modules/zfs.nix | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/modules/zfs.nix b/modules/zfs.nix
index e5e55b3..b2a9b6d 100644
--- a/modules/zfs.nix
+++ b/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" ];