Occasionally my Macbook Pro will slow down as the hard drive clicks away endlessly. CPU load is low, but applications and menuitems are slow to respond. Is there a utility that can help me determine what's going on, such as the number of bytes read/written or files open/closed per process, over time?
iotop tracks disk I/O by process, and prints a summary report that is refreshed every interval.
This is measuring disk events that have made it past system caches.
Since this uses DTrace, only the root user or users with the dtrace_kernel privilege can run this command.
This may not be precisely what you want - but it's a ksh script which wraps around dtrace, so you should be able to figure out how to make dtrace do what you need, if iotop doesn't handle it by default.
However, something like
iotop -C 5 12 should give you something to start with: it will output 12 samples, each 5 seconds long.
You can also use
fs_usage to get a blow-by-blow account of what apps are hitting the disk.
I always noticed this on Saturday mornings, and it turned out to be
locate, which updates its database at 3:15am on Friday nights.
I tried disabling its
launchd configuration (in
/System/Library/LaunchDaemons/com.apple.locate.plist), but it still ran anyway, so I just moved
/usr/libexec/locate.updatedb out of the way. Problem…mitigated.
It might be the OS paging to virtual memory instead of something application specific. You might try quitting less frequently used applications or at least restarting some applications that like to build up in-memory caches over time (e.g. Safari). Check out the various per-process memory statistics with Activity Monitor to find likely culprits. If quitting some memory intensive applications seems to temporarily alleviate the problem, you might try adding RAM.
If the disk activity is not paging related, you might be able to use
fs_usage to track it back to one or more specific processes.