云盘

A volume provides storage space for a VM instance. Volumes are categorized into root volumes and data volumes.
Note: Volume management mainly involves data volumes.

Concepts

  • Root volume: A root volume provides support for the system operations of a VM instance.
  • Data volume: A data volume provides extended storage space for a VM instance.

Considerations

  • A volume attached to a VM instance cannot be attached to a VM instance of another hypervisor type. For example, a volume attached to a KVM VM instance cannot be attached to a VMware VM instance.
  • The storage space that a volume takes up is calculated based on the virtual size of the volume. When a volume is created, the virtual size of the volume is deducted. The actual storage space that the volume takes up is small upon creation while increases along with growing data writes.
  • A non-shared volume can be attached to only one VM instance. A shared volume can be created on a Ceph primary storage and Shared Block primary storage and allows simultaneous access from multiple VM instances.
  • A root volume is an integral part of a VM instance. It cannot be detached from a VM instance.
  • A data volume attached to a VM instance can be detached from the VM instance and then attached to another VM instance of the same hypervisor type.
  • When multiple primary storages are available, you can specify a primary storage to create a volume. If you do not specify a primary storage when you create a volume:
    • For Local Storage primary storages, the volume is created on the primary storage with largest available space by default.
    • For NFS primary storages, the volume is created on a random primary storage by default.
    • For the combination of Local Storage and NFS primary storages or the combination of Local Storage and Shared Mount Point (SMP) primary storages, by default, the volume is created on the primary storage that the root volume of the VM instance to which the volume is attached does not reside.
  • You can set QoS for a data volume to limit disk bandwidth. Note that an excessively low QoS may greatly lower I/O performance.