From 8e0e9bdee874c3a3cdb50100f93f99c98ac7a7c6 Mon Sep 17 00:00:00 2001
From: Jonathan Davies <jpds@protonmail.com>
Date: Fri, 9 Feb 2024 15:03:47 +0000
Subject: [PATCH] nixos/zfs: Added a randomizedDelaySec option to ZFS
 autoscrub/trim timers

Allows operators to space out these IO operations across a fleet of
machines, rather than have them all happen at the same time.
---
 nixos/modules/tasks/filesystems/zfs.nix | 30 ++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/tasks/filesystems/zfs.nix b/nixos/modules/tasks/filesystems/zfs.nix
index 2c749d45d7a1..cf8ad94eea13 100644
--- a/nixos/modules/tasks/filesystems/zfs.nix
+++ b/nixos/modules/tasks/filesystems/zfs.nix
@@ -441,6 +441,18 @@ in
           {manpage}`systemd.time(7)`.
         '';
       };
+
+      randomizedDelaySec = mkOption {
+        default = "6h";
+        type = types.str;
+        example = "12h";
+        description = ''
+          Add a randomized delay before each ZFS trim.
+          The delay will be chosen between zero and this value.
+          This value must be a time span in the format specified by
+          {manpage}`systemd.time(7)`
+        '';
+      };
     };
 
     services.zfs.autoScrub = {
@@ -456,6 +468,18 @@ in
         '';
       };
 
+      randomizedDelaySec = mkOption {
+        default = "6h";
+        type = types.str;
+        example = "12h";
+        description = ''
+          Add a randomized delay before each ZFS autoscrub.
+          The delay will be chosen between zero and this value.
+          This value must be a time span in the format specified by
+          {manpage}`systemd.time(7)`
+        '';
+      };
+
       pools = mkOption {
         default = [];
         type = types.listOf types.str;
@@ -862,6 +886,7 @@ in
         timerConfig = {
           OnCalendar = cfgScrub.interval;
           Persistent = "yes";
+          RandomizedDelaySec = cfgScrub.randomizedDelaySec;
         };
       };
     })
@@ -879,7 +904,10 @@ in
         serviceConfig.ExecStart = "${pkgs.runtimeShell} -c 'for pool in $(zpool list -H -o name); do zpool trim $pool;  done || true' ";
       };
 
-      systemd.timers.zpool-trim.timerConfig.Persistent = "yes";
+      systemd.timers.zpool-trim.timerConfig = {
+        Persistent = "yes";
+        RandomizedDelaySec = cfgTrim.randomizedDelaySec;
+      };
     })
   ];
 }