"Instance": A virtual machine.
"Flavor": Hardware associated with "Instance". Such as RAM, CPU, disk.
There are two known types of storage for instances used in today's cloud services. One of them is ephemeral disk,in other words, short-lived temporary disk, and the other is persistent disk that is defined as permanent.
Ephemeral disks are temporary disks that are used by instance. Ephemeral storage is very useful for basic requirements such as operating system storage, but servers running on these disks are generally preferred for short-term use. Ephemeral disks are created with virtual machines, which means that these virtual disks will also be lost when the virtual machine is terminated. Therefore, this area is used to store contents where data loss is not significant.
However, persistent disk is durable, used with high performance and distributed block storage solution. It offers different IOPS (data read / write speed) options with SSD and HDD storage areas that can be added to instances, also allows for resizing and provides flexibility. Permanent disks can be connected to any instance and used as a permanent storage area for that instance. They are used completely independent of the instances they are connected to. Therefore, even if the virtual machine is deleted, the data can be stored or completely destroyed.
An instance which is opened on ephemeral disks does not have the elasticity of an instance that is running on permanent disks. Ephemeral disks can be damaged in some operations such as resize and migration due to their structure, therefore resizing is not recommended for instances created on local disks.
Q: Can the Ephemeral OS disk be resized?
A: No, the operating system disk cannot be resized after the ephemeral disk is provided.
Q: Can manageable block storage area be added to the virtual server that is built on the ephemeral disk?
A: Yes, block storage space can be added provided that it is independent of the server's OS disk.
Q: Can Ephemeral OS disk be created using Powershell or CLI?
A: Yes, you can create VMs with ephemeral OS disk using REST, templates, PowerShell and CLI.