How to run filesystem and RAW I/O's on RHEL / CentOS (Testing Purpose)

"dd" Command is used to monitor write performance of a disk on the Linux OS.

Typical DD syntex:

dd if=/dev/<input_file> of=/path/to/<output_file bs=<block-size> count=<number-of-blocks> <other_options>


Use the dd command to :

1. Measure server throughput (write speed)

dd if=/dev/zero of=/tmp/out-file1.img bs=1G count=1 oflag=dsync

Note: "oflag=dsync" option means use synchronized I/O for data. It doesn't use cache and gives accurate results

2. Measure server latency

dd if=/dev/zero of=/tmp/out-file1.img bs=512 count=1000 oflag=dsync

If you want to run RAW IO on a disk directly for long time you can run dd command in while loop loop;

# while true;do dd if=/dev/zero of=/dev/sdb bs=2048 count=5000 oflag=dsync;sync;done;

To come out of this loop use "Ctrl + C".