I did some basic dd tests to get an idea of the speed of multipath vs individual devices, some of the numbers seem not to make sense. I ran several test with dd, 4 at a time reading different parts of the device. multibus - round robin among paths rr_min_io=1, 4 paths individual - each dd going to a separate path dd with iflag=direct multibus : 120 MB/s individual : 115 MB/s dd without direct multibus : 44MB/s (why is this so bad) individual : 160MB/s (why is this so good) Why is multibus without direct the worst, yet individual devices without direct is the fastest. And why doesn't multibus perform about the same as going to the individual devices (25% performance hit using multibus)? Multibus is round-robin, how about a mode that sends io out on all paths simultaneously? Another thing I noticed during some of my test is that performance for a single dd will increase in the multibus mode as I up the blocksize parameter of dd. Thanks, Andy -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
