It is an block store (Data is split into evenly sized blocks)
Used to provision block storage to be used with VMs (Virtual Hard drives)

This storage can be directly accessed by the OS of the VM
Can only be used by 1 VM at a time
Has support for regional persistent disk (Data is replicated to an 2nd Zone)

Standard Tier
Standard Throughput
It is an HDD
Best for cost sensitive applications

Balanced Tier
Best price per GB
It is an SSD
Suitable for most workloads

Performance Tier
Best price per IOPS
It is an SSD
Suited for performance sensitive workloads

Extreme Tier
Best performance offering
It is an SSD