I have sysmon on my Linux systems. It is a nice graphical tool to show CPU, memory, and network loads. It produces strip charts. (It also does other things, but that's not my current concern.) When I want to figure out what's taking so long, sysmon is a handy tool. But I think that my system's bottleneck is often disk I/O. sysmon has no strip chart for that. I don't even know how it should be done: - each device should probably have a different trace, just like each processor core does - percentage would be ideal but I don't know what that would mean. Do you count I/O ops? Queue length? Processes waiting? + sequential I/O is much faster than random I/O (at least on a real disk). + Large operations are somewhat slower than small ones (generally speaking). + output is generally non-blocking (roughly: the write goes into the kernel's memory, queued for writing to the device, and the process proceeds without waiting to the write to actually complete) + input usually blocks: the process issues a read and waits until the read finishes before it proceeds + Perhaps the simplest metric might be the number of processes waiting for disk I/O completion. But that leaves writes unaccounted for. Do you have any suggestions for a simple (possibly simplistic) tool to show disk bottlenecks in real time? PS: On the system I'm looking at, in the sysmon pane for "Processes", there is a column for "Disk read total" and another for "Disk write total". After a day of running the Libreswan test suite, gnome-terminal server wins with 3.4GiB of read and 3.9GiB of write. I wonder what that's all about. I would not expect Gnome Terminal to do disk I/O. As it happens, essentially all the output to the terminal is being captured by a script(1) command (run within the gnome terminal session). It shows 11.4MiB of disk output for one complete run, which should be half or a third of all that has gone to Gnome Terminal because I've run the suite two or three times since logging in. But it is more like a 11.4/3400 or roughly 1/300. Guess: gnome terminal reads and writes to X count as disk I/O. That's pretty messed up.