Not quite exactly what the OP was looking for but the use of dd isn't a best practice in my opinion.
DD is on the whole just much better used for imaging disks than benchmarking. Use Fio.
sudo dnf install fio or
sudo apt-get install fio
4k random test
fio --filename=/dev/sdx --direct=1 --rw=randrw --refill_buffers --norandommap --randrepeat=0 --ioengine=libaio --bs=4k --rwmixread=100 --iodepth=16 --numjobs=16 --runtime=60 --group_reporting --name=4ktest
8k mixed test
fio --filename=/dev/sdx --direct=1 --rw=randrw --refill_buffers --norandommap --randrepeat=0 --ioengine=libaio --bs=8k --rwmixread=70 --iodepth=16 --numjobs=16 --runtime=60 --group_reporting --name=8k7030test
taken from: http://www.storagereview.com/fio_flexible_i_o_tester_synthetic_benchmark
once you are sure your raw disks are performing as they should, create the raid-0 unit via madam and then before partitioning test them again but this time instead of /dev/sd{x} pass in whatever you called your raid array, once satisfied, create your partitions aligning as needed and test that, then once good there, format and mount and test that.
dd
to access the disk directly, or are you going through the filesystem by reading/writing a file?dd if=/dev/sda of=/dev/null bs=8k count=100k
, whereif=
is the path to your SSD RAID device.