Throughput throttling on Azure VM We are just entering Azure world and will be migrating SQL server soon.I am trying to test throughput on Azure VM (DS13_V2) which is supposed to give 384MB/Sec as per documentation.

Here is the configuration : 

a) No of cores : 8 

b) Attached 2 disks (1TB each formatted with 64K block size) to the VM which          are P30 disks(200mb/sec).

c) I have striped 2 disks into one and called it F: drive with total 2TB which in theory is capable of giving 400mb/sec.

Test:
I ran SQLIO (with Test file size - 20GB on the striped drive F:) with multiple combinations and looks like throughput is throttled at 256mb/sec consistently.
I even ran diskspd which also gives me the same 256mb/sec throughput.  

Question:
I am wondering where the bottleneck is or anything that i am missing as VM is capable of giving 384mb/sec and my striped disks are capable of giving 400mb/sec (200mb/sec each) wherein i should be seeing a throughput of 384mb/sec.

Please let me know if any suggestions would help me in doing a better storage test.
Those numbers in your performance tests are accurate. Theoretical throughput does not match my experience, after migrating an environment to more than ten DS13v2 instances. I get between 220MB/s and 256MB/s, depending on the type of writes, even with P30s.

To answer your question, the bottleneck is the network itself, which links the drives to the VM.