Monitoring DISKIO for elasticsearch in Windows

How do I say my DISK IO is a bottleneck?
I'm using AZURE VMs for elastic search in Windows OS. In each VM, I attach a data drive (F:), which is derived of storage pool using 2 physical disks. These disks are not SSD's. When I restart the node, I see lot of elastic search operations going on with disks performing assignment of shards. I see the disk reads/writes @ around 30MB/Sec. Is it expected. The node has around 120GB of data with 23 shards.

The confusion is because according to azure documentation, if I use 2 disks (2blobs) it should be 60+60 120MBPS at the rate of 1000 requests/sec.

Kindly clarify