us:~$? dd if=/dev/zero of=./a.dat bs=1M count=8k oflag=direct

8192+0 records in

8192+0 records out

8589934592 bytes (8.6 GB, 8.0 GiB) copied, 25.5874 s, 336 MB/s

orangepi@orangepi5plus:~$? dd if=/dev/zero of=./a.dat bs=1M count=4k

4096+0 records in

4096+0 records out

4294967296 bytes (4.3 GB, 4.0 GiB) copied, 11.5054 s, 373 MB/s

orangepi@orangepi5plus:~$? dd if=/dev/zero of=./a.dat bs=4k count=2M oflag=direct

2097152+0 records in

2097152+0 records out

8589934592 bytes (8.6 GB, 8.0 GiB) copied, 185.458 s, 46.3 MB/s

orangepi@orangepi5plus:~$ dd if=/dev/zero of=./a.dat bs=4k count=20000

20000+0 records in

20000+0 records out

81920000 bytes (82 MB, 78 MiB) copied, 0.198936 s, 412 MB/s

orangepi@orangepi5plus:~$ dd if=/dev/zero of=./a.dat bs=4k count=200000

200000+0 records in

200000+0 records out

819200000 bytes (819 MB, 781 MiB) copied, 2.03001 s, 404 MB/s

orangepi@orangepi5plus:~$ dd if=/dev/zero of=./a.dat bs=4k count=400000

400000+0 records in

400000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 3.23551 s, 506 MB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=400000? iflag=direct

400000+0 records in

400000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 41.8229 s, 39.2 MB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=40000

40000+0 records in

40000+0 records out

163840000 bytes (164 MB, 156 MiB) copied, 0.149626 s, 1.1 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=80000

80000+0 records in

80000+0 records out

327680000 bytes (328 MB, 312 MiB) copied, 0.130862 s, 2.5 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=80000

80000+0 records in

80000+0 records out

327680000 bytes (328 MB, 312 MiB) copied, 0.137194 s, 2.4 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=200000

200000+0 records in

200000+0 records out

819200000 bytes (819 MB, 781 MiB) copied, 0.262883 s, 3.1 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=2M

400000+0 records in

400000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 0.591919 s, 2.8 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=4k count=40000 iflag=direct

40000+0 records in

40000+0 records out

163840000 bytes (164 MB, 156 MiB) copied, 2.84328 s, 57.6 MB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=8k count=40000

40000+0 records in

40000+0 records out

327680000 bytes (328 MB, 312 MiB) copied, 0.164237 s, 2.0 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=8k count=200000

200000+0 records in

200000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 0.412878 s, 4.0 GB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=8k count=200000? oflag=direct

dd: failed to open '/dev/null': Invalid argument

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=8k count=200000? iflag=direct

200000+0 records in

200000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 14.2196 s, 115 MB/s

orangepi@orangepi5plus:~$ dd if=./a.dat of=/dev/null bs=8k count=200000? iflag=direct

200000+0 records in

200000+0 records out

1638400000 bytes (1.6 GB, 1.5 GiB) copied, 14.3662 s, 114 MB/s

orangepi@orangepi5plus:~$

?sudo hdparm -Tt /dev/nvme0n1p2

[sudo] password for orangepi:

/dev/nvme0n1p2:

?Timing cached reads:? ?7408 MB in? 2.00 seconds = 3706.98 MB/sec

?Timing buffered disk reads: 1176 MB in? 3.00 seconds = 391.42 MB/sec