Q. Does Azure Premium Storage use sparse storage?
A. Regular Azure storage uses sparse storage. This means if a 1 TB fixed-size virtual hard disk (VHD) is created, but only 100 MB of data is written on the Azure fabric, then only 100 MB of data is actually written to the storage fabric* and you are only charged for 100 MB.
Azure Premium Storage works differently: you pay for the type of Azure Premium Storage disk you buy, regardless of how much data is written to it, because you are buying a predictable performance rather than a maximum performance.
At time of my writing this, there are 3 types of Azure Premium Storage disk, the P10, P20 and P30 as shown below.
| Premium Storage Disk Type | P10 | P20 | P30 |
| Disk Size | 128 GB | 512 GB | 1024 GB |
| IOPS per disk | 500 | 2300 | 5000 |
| Throughput per disk | 100 MB per second | 150 MB per second | 200 MB per second |
| Price per month (exact price may vary) | $17.92 | $66.56 | $122.88 |
For the most current pricing see http://azure.microsoft.com/en-us/pricing/details/storage/.
When using the Azure portal you can only select one of the sizes listed above as shown below. If using PowerShell you can create other sizes however the actual performance allocation and billing will be rounded up to a specific Premium Storage disk type, i.e. if you create a 200 GB disk it will actually have the performance and billing of a P20 (512 GB). If you only write 10 MB of data you still pay the monthly price of that P20.
* Actually 300 MB of data is written to the storage fabric, since all data is stored at least 3 times for resiliency, but you only get charged for the 100 MB of data you're storing.
