Alice and Bob in I/O Land

One property of disks - is that they work better sequentially, fetching large amounts of data.
One property of applications - is their tendency to perform sequential I/O.
Thus, devices (and file-systems) are often configured to perform read-ahead.
The "read-ahead" is sent immediately after the application read...
...and returns quickly after.
Thus, when the application will want to read the next page - we'll find it in the cache.
If the application won't need the next pages - we wasted disk bandwidth...
...and possibly evicted other cached pages from memory.
Thus, for applications that perform random reads - read-ahead is a bad feature.

Originally written by