If you have a 100 GB VHD but have only 50 MB of data written to it, you only pay for 50 MB of data. This means you should always create your data disks as 1,023 GB, the maximum. It’s difficult to resize a disk post-creation on regular Azure Storage. Additionally, Azure Storage supports TRIM. When data is deleted, that deletion flows through to the underlying Azure Storage. Almost like shrinking a VHD, you no longer pay for deleted space.
Don't mess with VHD sizes. Use maximum. Simplify, simplify...
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