Incorrect DD readings? No IOstat activity.

[helloha]

I'm testing the performance of a single disk in my setup using DD.

It says i'm writing at 430Mb/s which is impossible. (It's a seagate ST4000DM000 running at 5900 rpm).

It only shows a few Mb/s in writes using iostat.

But the file is still being created and it has the correct size (after 993.575445 seconds there was a 400GB file on the disk).

Does anyone know what is going on?

K.

Code:

 pool: TEST-4TB
 state: ONLINE
  scan: none requested
config:

    NAME                                          STATE     READ WRITE CKSUM
    TEST-4TB                                      ONLINE       0     0     0
      gptid/b906c02c-5f8a-11e5-beef-001f2954783c  ONLINE       0     0     0

errors: No known data errors

Code:

kareldc@SERVER:/mnt/TEST-4TB % sudo dd if=/dev/zero of=/mnt/TEST-4TB/testfile bs=1G count=400
400+0 records in
400+0 records out
429496729600 bytes transferred in 993.575445 secs (432273897 bytes/sec)

 

[helloha]

Then I noticed that lz4 compression was enabled... all cleared up!