On Wed, Feb 01, 2012 at 07:06:35AM +1100, Dave Chinner wrote: > The number of IOs does not equal the number of seeks. Two adjacent, > sequential IOs issued serially will show up as two IOs, even though > there was no seek in between. Especially if the files are large > enough that readahead tops out (500-800k is large enough for this as > readahead maximum is 128k by default). So it might be taking 3-4 > IOs just to read the file data. Ah. And if the IOs are not stacked up, then the platter has to rotate nearly a whole turn to perform the next one. > > So the next thing I'd have to do is to try to get a trace of the I/O > > operations being performed, and I don't know how to do that. > > blktrace/blkparse or seekwatcher. Excellent, just what I wanted. I've made a start with this and will report back. Many thanks for the help and pointers you have provided. Regards, Brian. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
