
4.9 Fundamentals of storage performance 317
Chapter 4
disk itself, it can involve reading a single track, or for some implementa-
tions, reading an entire cylinder (i.e., tracks from each platter making up
the disk drive). This can force the controller to fetch much more data than
what was actually requested; some implementations will collect a minimum
256 KB of data, whatever the actual requested I/O size. The controller will
store this fetched data into cache memory (hence it will tend to require
more cache than otherwise optimized controllers) and hope that this data
will be used in subsequent operations. In that case, big caches are good and
useful. ...