Raw Device Mapping (RDM) Datastore¶
The RDM Datastore is an Image Datastore that enables raw access to block devices on Nodes. This Datastore enables fast VM deployments due to a non-existent transfer operation from the Image Datastore to the System Datastore.
The Datastore should only be usable by the administrators. Letting users create images in this Datastore is a huge security risk! For example, users could register an image
/dev/sda and read the Host filesystem.
The RDM Datastore is used to register already existing block devices on the Nodes. The devices should be already set up and available, and VMs using these devices must be enforced to run on the Nodes ready for them. Additional Virtual Machine files, like deployment files or volatile disks, are created as regular files.
No additional setup is required. Make sure /etc/one/oned.conf has the following configuration for the RDM Datastore:
TM_MAD_CONF = [ NAME = "dev", LN_TARGET = "NONE", CLONE_TARGET = "NONE", SHARED = "YES", TM_MAD_SYSTEM = "ssh,shared", LN_TARGET_SSH = "SYSTEM", LN_TARGET_SHARED = "NONE", DISK_TYPE_SSH = "FILE", DISK_TYPE_SHARED = "FILE", CLONE_TARGET_SSH = "SYSTEM", CLONE_TARGET_SHARED = "SELF", DRIVER = "raw" ]
The devices you want to attach to a VM should be accessible by the hypervisor. KVM usually runs under the identity of
oneadmin user; make sure this user is in a group with access to the disk (like
disk) and has read write permissions for the group.
Once the Node storage setup is ready, the OpenNebula configuration comprises two steps:
- Create System Datastore
- Create Image Datastore
Create System Datastore¶
The RDM Datastore can work with the following System Datastores:
Note that the System Datastore is only used for volatile disks and context devices.
Create Image Datastore¶
To create an Image Datastore, you need to set following (template) parameters:
||Name of Datastore|
An example template of Datastore:
$ cat rdm.conf NAME = rdm_datastore TYPE = "IMAGE_DS" DS_MAD = "dev" TM_MAD = "dev" DISK_TYPE = "BLOCK" $ onedatastore create rdm.conf ID: 101
New images can be added just like any other image by specifying the path. As an example, here is an image template to add a Node disk
$ cat image.tmpl NAME=scsi_device PATH=/dev/sdb PERSISTENT=YES $ oneimage create image.tmpl -d 101
If you are using the CLI, pass the absolute path to the device with parameter
oneimage create -d 101 --name nbd --source /dev/sdc --driver raw --prefix vd --persistent --type OS --size 0MB
As this Datastore is just a container for existing devices, the size of images in OpenNebula doesn’t reflect the real block device size. All devices registered will render a size of 0 and the overall devices Datastore will show up with 1MB of available space