$ cat /sys/block/sda/queue/read_ahead_kb
By default my Ubuntu 12.04 system has 256 as read_ahead value that means only 128KB of data is read in advance from the cache memory before the application needs it. You can use the below mentioned commands to get the “read ahead” default value in your system.
$ sudo blockdev --setra 1024 /dev/sda
Generally, every computer's task is to either read a block of data from the disk and move it to RAM or write a new block of data from the RAM to the disk. These tasks are called as the read/write requests or the I/O requests.
Linux has four different I/O schedulers namely noop, deadline, anticipatory and cfq, whereas Ubuntu 12.04 includes all except anticipatory scheduler. These schedulers sort the incoming I/O requests in a queue for optimizing the load. So, the /sys/block/sda/queue/nr_requests parameter defines the queue size or queue length. The default value assigned to this parameter is 128 which can be changed to 1024 using the below mentioned command.