dd

To test speed of hard disk, run

dd if=/dev/zero of=serverok bs=64k count=16k conv=fdatasync

Here is test result for 2 * SSD

root@india ~ # dd if=/dev/zero of=serverok bs=64k count=16k conv=fdatasync
16384+0 records in
16384+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 2.58697 s, 415 MB/s
root@india ~ # 

Write ISO into USB Drive

dd bs=4M if=/mnt/data/archlinux-2018.06.01-x86_64.iso of=/dev/sde1 status=progress oflag=sync