The difference between SSD and HDD drives in Azure is that SSD storage equipment is provided at a higher cost, as part of the Premium storage tier. For example, Premium Managed Disks (SSD) start from $0.6 per month for 4GB, while Standard Managed Disks (HDD) start from $0.3 per month for 4GB. SSD provides higher performance that can support mission critical and high throughput workloads. Read more about Difference Between SSD and HDD in Azure