Overview

Datastore Types

OpenNebula storage is structured around the Datastore concept. A Datastore is any storage medium to store disk images. OpenNebula features three different datastore types:

  • The Images Datastore, stores the images repository.
  • The System Datastore holds disk for running virtual machines. Disk are moved, or cloned to/from the Images datastore when the VMs are deployed or terminated; or when disks are attached or snapshotted.
  • The Files & Kernels Datastore to store plain files and not disk images. The plain files can be used as kernels, ram-disks or context files. See details here.

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Image Datastores

There are different Image Datastores depending on how the images are stored on the underlying storage technology:

  • Filesystem, to store images in a file form.
  • LVM, to store images in LVM logical volumes.
  • Ceph, to store images using Ceph block devices.
  • Raw Device Mapping, to direct attach to the virtual machine existing block devices in the nodes.
  • iSCSI - Libvirt Datastore, to access iSCSI devices through the buil-in qemu support.

Disk images are transferred between the Image and System datastores by the transfer manager (TM) drivers. These drivers are specialized pieces of software that perform low-level storage operations. The following table summarizes the available transfer modes for each datastore:

Datastore Image to System Datastore disk transfers methods
Filesystem
  • shared, images are exported in a shared filesystem
  • ssh, images are copied using the ssh protocol
  • qcow2, like shared but specialized for the qcow2 format
Ceph
  • ceph, all images are exported in Ceph pools
  • shared, volatile & context disks exported in a shared FS.
LVM
  • fs_lvm, images exported in a shared FS but dumped to a LV
Raw Devices
  • dev, images are existing block devices in the nodes
iSCSI libvirt
  • iscsi, images are iSCSI targets

How Should I Read This Chapter

Before reading this chapter make sure you have read the Open Cloud Host chapter. After that, proceed to the specific section for the Datastores you may be interested in.

After reading this chapter you should read the Open Cloud Networking chapter.

Hypervisor Compatibility

This chapter applies only to KVM.

Follow the vCenter Storage section for a similar guide for vCenter.