Move megacli2prom to a place where only the machines with such cards use it

morph/grid/production/grid.nix

@@ -70,6 +70,10 @@ let
       # Slightly awkwardly, enable some of our hardware / network / bootloader options.
       ../../../nixos/modules/100tb.nix
 
+      # At least some of our storage nodes utilize MegaRAID storage controllers.
+      # Monitor their array status.
+      ../../../nixos/modules/monitoring/exporters/megacli2prom.nix
+
       # Get all of the configuration that is common across all storage nodes.
       gridlib.storage
 
@@ -88,6 +92,10 @@ let
     # name is quoted because `1` makes `100tb` look an awful lot like a
     # number.
    "100tb".config = nodecfg;
+
+    # Enable statistics gathering for MegaRAID cards.
+    # TODO would be nice to enable only on machines that have such a device.
+    services.private-storage.monitoring.megacli2prom.enable = true;
   };
 
   # Define all of the storage nodes for this grid.

morph/lib/storage.nix

@@ -43,14 +43,8 @@ in {
     ../../nixos/modules/monitoring/vpn/client.nix
     # Expose base system metrics over the monitoringvpn.
     ../../nixos/modules/monitoring/exporters/node.nix
-    # At least some of our storage nodes utilize MegaRAID storage controllers.
-    ../../nixos/modules/monitoring/exporters/megacli2prom.nix
   ];
 
-  # Enable statistics gathering for MegaRAID cards.
-  # TODO would be nice to enable only on machines that have such a device.
-  services.private-storage.monitoring.megacli2prom.enable = true;
-
   # Turn on the Private Storage (Tahoe-LAFS) service.
   services.private-storage = {
     # Yep.  Turn it on.