Recently we ordered a few servers with soft raid1, but seems the soft raid doesn't perform well, copy a 1G file, it takes about 40 seconds.

also sometimes it takes very very long time, I haven't count it, at least a few minutes, just like the server is dead.

I have run this command.
dd if=/dev/zero of=test.bin bs=1000M count=1
1+0 records in
1+0 records out
1048576000 bytes (1.0 GB) copied, 1.14416 seconds, 916 MB/s

But obviously it takes more more than 1 second, why it shows only takes 1 second?

I'm using two ST31000528AS hard disks.
Any suggestions?