Tools

dd
hdparm
iotop

FIO

Tool for benchmarking IO. Can spawn multiple threads performing different kind of work.

Options worth mentioning:
direct=<bool> - uses non-buffered IO (O_DIRECT)

Testing scenarios

Random read-write

fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=random_read_write.fio --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75

References

1. https://dotlayer.com/how-to-use-fio-to-measure-disk-performance-in-linux/
2. https://wiki.mikejung.biz/Benchmarking#Fio_Test_Options_and_Examples