Block Storage - Concepts
A block device is a storage volume on a network-connected storage system that is exposed to the guest operating system as if it were a physical disk.
The boot-on-block feature allows Instances to boot from attached Block Storage volumes instead of local volumes. This feature is available for all Instance types.
The local volume of an Instance is an all SSD-based storage solution, using a RAID array for redundancy and performance, that is hosted on the local hypervisor.
Storage Area Networks (SANs)
A Storage Area Network (SAN) consists of interconnected machines, network infrastructure and storage devices designed for performance and high-availability. Unlike a Network Attached Storage (NAS) which stores all data on a file level, the SAN stores all data on block level, this makes SAN a perfect solution for business critical applications and input/output intense operations like relational databases. The SAN is a network-connected solution, that operates independently from the local hypervisor hosting the virtual Instance. The storage capacity of the block devices on the SAN can be tailored towards your requirements.