Google Cloud Persistent Disks

Persistent disks are durable network storage devices that the VM instances can access like physical disks
The data on each persistent disk is distributed across several physical disks
Compute Engine manages the physical disks and the data distribution for the customer to ensure redundancy and optimal performance
There are 2 types of persistent disks - Standard persistent disks that are based by hard disk drives (HDD) and SSD persistent disks that are backed by solid-state drives (SSD)
Standard persistent disks are efficient and economical for handling sequential read/write operations, but are not optimized to handle high rates of random input/output operations per second (IOPS)
For applications that require high rates of random IOPS, use SSD persistent disks
Persistent disks are located independently from the VM instances, so the customer can detach or move persistent disks to keep their data even after they delete their VM instances
Persistent disk performance scales automatically with size, so the customer can resize their existing persistent disks or add more persistent disks to an instance to meet their performance and storage space requirements
Compute Engine handles most disk management tasks for the customer so that they do not need to deal with partitioning, redundant disk arrays, or subvolume management
Each persistent disk can be up to 64 TB in size
Most instances can have up to 128 persistent disks and up to 257 TB of total persistent disk space attached per instance
A customer can save time and get the best performance if they format their persistent disks with a single file system and no partition tables
A customer is recommended to attach multiple secondary disks only when they need to separate their data into unique partitions
Persistent disk performance is predictable and scales linearly with provisioned capacity until the limits for an instance's provisioned vCPUs are reached
When a customer needs more disk space or better performance, they resize their disks and possibly add more vCPUs to add more storage space, throughput, and IOPS
Persistent disk performance is based on the total persistent disk capacity attached to an instance and the number of vCPUs that the instance has

Each persistent disk write operation contributes to the cumulative network egress traffic for the VM instance
Checksums are calculated for all persistent disk operations to ensure data integrity
Compute Engine automatically encrypts customers data before it travels outside of their VM instance to persistent disk storage space
When a customer deletes a persistent disk, Google discards the cipher keys, rendering the data irretrievable and this process is irreversible
Regional persistent disks provide durable storage and replication of data between two zones in the same region
Regional persistent disks provide synchronous replication for workloads that might not have application-level replication
Regional persistent disks are an option for high performance databases and enterprise apps that also require high availability