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Is there a command to test the hard disk speed ?

You can use: You should see something like this:
/dev/sda:
Timing cached reads: 15132 MB in 1.99 seconds = 7586.99 MB/sec
Timing buffered disk reads: 330 MB in 3.00 seconds = 109.86 MB/sec

or for M2 SSD:
/dev/nvme0n1p2:
Timing cached reads: 17356 MB in 2.00 seconds = 8698.70 MB/sec
Timing buffered disk reads: 1952 MB in 2.76 seconds = 706.04 MB/sec