Index: sys/contrib/openzfs/module/os/freebsd/zfs/sysctl_os.c
===================================================================
--- sys/contrib/openzfs/module/os/freebsd/zfs/sysctl_os.c
+++ sys/contrib/openzfs/module/os/freebsd/zfs/sysctl_os.c
@@ -163,6 +163,13 @@
 	return (0);
 }
 
+static void
+warn_deprecated_sysctl(const char *name)
+{
+	printf("WARNING: sysctl vfs.zfs.%s is deprecated. Use vfs.zfs.vdev.%s instead.\n",
+	    name, name);
+}
+
 int
 param_set_arc_max(SYSCTL_HANDLER_ARGS)
 {
@@ -185,12 +192,15 @@
 	if (val != 0)
 		zfs_arc_max = arc_c_max;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("arc_max");
+
 	return (0);
 }
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_max,
 	CTLTYPE_ULONG | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-	NULL, 0, param_set_arc_max, "LU",
+	NULL, 1, param_set_arc_max, "LU",
 	"Maximum ARC size in bytes (LEGACY)");
 
 int
@@ -214,12 +224,15 @@
 	if (val != 0)
 		zfs_arc_min = arc_c_min;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("arc_min");
+
 	return (0);
 }
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_min,
 	CTLTYPE_ULONG | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-	NULL, 0, param_set_arc_min, "LU",
+	NULL, 1, param_set_arc_min, "LU",
 	"Minimum ARC size in bytes (LEGACY)");
 
 extern uint_t zfs_arc_free_target;
@@ -242,6 +255,9 @@
 
 	zfs_arc_free_target = val;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("arc_free_target");
+
 	return (0);
 }
 
@@ -251,7 +267,7 @@
  */
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_free_target,
 	CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE,
-	NULL, 0, param_set_arc_free_target, "IU",
+	NULL, 1, param_set_arc_free_target, "IU",
 	"Desired number of free pages below which ARC triggers reclaim"
 	" (LEGACY)");
 
@@ -270,12 +286,15 @@
 
 	arc_no_grow_shift = val;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("arc_no_grow_shift");
+
 	return (0);
 }
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_no_grow_shift,
 	CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-	NULL, 0, param_set_arc_no_grow_shift, "I",
+	NULL, 1, param_set_arc_no_grow_shift, "I",
 	"log2(fraction of ARC which must be free to allow growing) (LEGACY)");
 
 extern uint64_t l2arc_write_max;
@@ -746,12 +765,14 @@
 
 	zfs_vdev_min_auto_ashift = val;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("min_auto_ashift");
+
 	return (0);
 }
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, min_auto_ashift,
-	CTLTYPE_UINT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-	&zfs_vdev_min_auto_ashift, sizeof (zfs_vdev_min_auto_ashift),
+	CTLTYPE_UINT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, NULL, 1,
 	param_set_min_auto_ashift, "IU",
 	"Min ashift used when creating new top-level vdev. (LEGACY)");
 
@@ -771,12 +792,14 @@
 
 	zfs_vdev_max_auto_ashift = val;
 
+	if (arg2 != 0)
+		warn_deprecated_sysctl("max_auto_ashift");
+
 	return (0);
 }
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, max_auto_ashift,
-	CTLTYPE_UINT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-	&zfs_vdev_max_auto_ashift, sizeof (zfs_vdev_max_auto_ashift),
+	CTLTYPE_UINT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, NULL, 1,
 	param_set_max_auto_ashift, "IU",
 	"Max ashift used when optimizing for logical -> physical sector size on"
 	" new top-level vdevs. (LEGACY)");