Both runs have been done on a single 120GB 7200rpm IDE disk. Command used: iostat -x 5 (extended statistics, sample every 5 seconds).
iostat is a command line I/O performance monitoring utility. It is present in almost every major Unix flavor in use today, and here you can get the version for Linux.
It works on both 2.4 & 2.6. What makes it different from other Linux utilities, which mostly show only I/O transfer rates, is that you finally can get important information about disk utilization, number of requests, average queue size and disk & queue wait times. No serious sysadmin should be without it. Check the screenshots to learn more.
All screenshots were taken on my home workstation (Dual PIII 1GHz, 768MB RAM). Brown color represents kernel memory usage (miscellaneous caches), red is for active memory (page/buffer cache in use and mapped pages - applications), yellow is inactive page/buffer cache, green is free memory and finally orange color represents swap usage.
On the first picture you can see what happens when cron runs updatedb process, refreshing file name database (used by locate command). Rather quickly memory gets consumed by various kernel caches as updatedb traverses filesystems. Those are mostly inode & dentry caches, used by the kernel to find and access a file. Obviously, I have lots of files as more than half of my memory gets used by the caches. If you had enough memory so that you can cache and keep all this valuable information in memory, second updatedb run would finish almost instantly, instead of few minutes of disk crunching.
This utility provides you with a neat X11 window to monitor memory utilization of your server or workstation. It is similar to the popular xmem utility but is IMHO slightly more appropriate for monitoring a modern Linux VM subsystem (2.4 kernel and up).
It gathers information from miscellaneous /proc virtual files and shows you a graphical representation of the current memory utilization as distributed to inactive & active page lists and kernel memory (which includes inode & dentry caches). Additionally, it shows you how much swap is used. Please check screenshots together with comments to learn more.