Random and Sequential Data Access

 

These simple terms sometimes become mind boggling, Comparing random versus sequential operations is one way of assessing application efficiency in terms of disk use. Accessing data sequentially is much faster than accessing it randomly because of the way in which the disk hardware works.

Going back to basics - seek time measures the time it takes the head assembly on the actuator arm to travel to the track of the disk where the data will be read or written.

 

Sequential means – Data is linear and less seek operations are required

Random means – During read I/O, more seek operations are required

For workloads of either random or sequential I/O, use drives with faster rotational speeds. For workloads that are predominantly random I/O, use a drive with faster seek time. Sequential I/O on conventional disks can generally be served at a higher throughput because conventional disks can avoid almost all rotational delay and seek time penalties. Random I/O will always incur these penalties, at a varying rate.

 Following table shows examples of typical access patterns of various applications :