writing pseudo-random data to disks

[yudi v <yudi.tux@gmail.com>]

I am using the below command/s to write to 3TB hitachi deskstar 7200RPM disks.

dcfldd if=/dev/urandom status=off | PV -s 3000G | dcfldd of=/dev/sda of=/dev/sda of=/dev/sdb status=off bs=4096

on the HP microserver nl40 with SATA 3Gbps connection, the throughput was 3-4MB/s, around 10.5 days.

Where as on my desktop with i5 CPU and 6Gbps connection, the throughput is 13-14MB/s, around 61 hours.

My question is: where is the bottleneck on the HP for such low throughput?

dcfldd uses one core, granted my desktop is around 4Ghz and HP just under 2Ghz. But....

So far I have heard lot of people say the SATA connection should not make any difference to the throughput on a spindle HDD.

Anyone know the reason for such low throughput on HP?

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Kind regards,
Yudi