Performance means how long it takes for your customers to read and write
their data. If the storage service you provide is too slow, your customers will
find a way to work around it, perhaps by attaching extra disks to their own
desktops or by complaining to management.
The most important rule of optimization is to measure first, optimize
based on what was observed, and then measure again. Often, we see SAs optimize
based on guesses of what is slowing a system down. Measuring means
using operating system tools to collect data, such as which disks are the most
busy or the percentage of reads versus writes. Some SAs do not measure
but simply try various techniques until they find one that solves the performance
problem. These SAs waste a lot of time with solutions that do not produce
results. We call this technique blind guessing and do not recommend it.
Watching the disk lights during peak load times is a better measurement than
nothing.
The primary tools that a SA has to optimize performance are RAM and
spindles. RAM is faster than disk.With more RAM, one can cache more and
use the disk less. With more spindles (independent disks), the load can be
spread out over more disks working in parallel.