I've seen in many places that throughput = bs * iops should be true. For example writing at 128k block size to a SAS disk that can support 190 IOPS should give a throughput of ~23 MBps - 23.75(MBs) = 128(BS)*190(SAS-15 IOPS)/1024.

Now when I tested it in a VM against a monster NetApp filer I got theses results:

# dd if=/dev/zero of=/tmp/dd.out bs=4k count=2097152
8589934592 bytes (8.6 GB) copied, 61.5996 seconds, 139 MB/s

To view the IO rate of the VM I used iostat and esxtop, and they both showed around 250 IOPS.

So to my understanding the throughput was supposed to be ~1000k: 1000(KBs) = 4(BS)*250(IOPS).

dd of 8GB is twice the size of RAM of course, so no page caching here.

What am I missing?

Thanks!