On Mon, Sep 26, 2011 at 2:02 PM, Nicolas Ross <rossnick-lists at cybercat.ca> wrote: >>>> Not sure what those do, but lsof should show what files are open, and >>>> 'strace -p process_id' would show the system calls issued by a >>>> process. >>> >>> Thanks, that might be usefull. I'ill just have to find a way to strace >>> multiple process at once and find the usefull info among that load of >>> data... >> >> Note that if what is really happening is that different processes are >> frequently accessing the same disk in different locations (a fairly >> likely scenario) the time will be mostly taken by the head seeks in >> between and may be hard to pin down. > > I found the -f option to strace is able to attach to the forked child of a > parent process, so I will be using that in my debuging in conjunction > witgh -e to filter out only the calls I want to see... > > But indeed, that might be hard to find. In one case, I want to see what > files are opened / accessed on a gfs2 volume over a fiber channel link to a > raid-1 array, and the controler is supposed to intelligent enough to > distribute the read access across the 2 disks. And in the other case, it's > an ssd, so seek time should be 0. Not sure how gfs2 deals with client caching, but in other scenarios it's probably easier to just throw a lot of ram in the system and let the filesystem cache do its job. You still have to deal with applications that need to fsync(), though. -- Les Mikesell lesmikesell at gmail.com