- Tune down read_max. For single disks we get no gain out of reading more

than a MAXPHYS size block ahead.  Having this set too high just leaves
   other processes starved for IO and screws up interactive response.  Let the
   users with RAID set it higher when they need it.

sys/kern/vfs_cluster.c

@@ -73,7 +73,7 @@ static int write_behind = 1;
 SYSCTL_INT(_vfs, OID_AUTO, write_behind, CTLFLAG_RW, &write_behind, 0,
     "Cluster write-behind; 0: disable, 1: enable, 2: backed off");
 
-static int read_max = 64;
+static int read_max = 8;
 SYSCTL_INT(_vfs, OID_AUTO, read_max, CTLFLAG_RW, &read_max, 0,
     "Cluster read-ahead max block count");