Datastores

Types

OpenNebula features three different datastore types:

The Image Datastore stores the Image repository.
The System Datastore holds disk for running Virtual Machines, usually cloned from the Image Datastore.
The Files & Kernels Datastore to store plain files used in contextualization, or VM kernels used by some hypervisors.

By default, OpenNebula will create an image (default), system (system), and files datastore (files). These datastores are configured to use the SSH protocol to transfer images. You can list the datastores in your cloud with the onedatastore list command:

$ onedatastore list
  ID NAME                SIZE AVA CLUSTERS IMAGES TYPE DS      TM      STAT
   2 files                50G 86% 0             0 fil  fs      local   on
   1 default              50G 86% 0             2 img  fs      local   on
   0 system                 - -   0             0 sys  -       local   on

Attributes

Image and Files & Kernels Datastores

You can access the information about each datastore using the onedatastore show command. For example the information of your default datastore may look like:

$ onedatastore show 1
DATASTORE 1 INFORMATION
ID             : 1
NAME           : default
USER           : oneadmin
GROUP          : oneadmin
CLUSTERS       : 0
TYPE           : IMAGE
DS_MAD         : fs
TM_MAD         : local
BASE PATH      : /var/lib/one//datastores/1
DISK_TYPE      : FILE
STATE          : READY

DATASTORE CAPACITY
TOTAL:         : 50G
FREE:          : 43.2G
USED:          : 6.8G
LIMIT:         : -

PERMISSIONS
OWNER          : um-
GROUP          : u--
OTHER          : ---

DATASTORE TEMPLATE
ALLOW_ORPHANS="YES"
CLONE_TARGET="SYSTEM"
DISK_TYPE="FILE"
DS_MAD="fs"
LN_TARGET="SYSTEM"
RESTRICTED_DIRS="/"
SAFE_DIRS="/"
TM_MAD="local"
TYPE="IMAGE_DS"

IMAGES
0
1

There are four important sections:

General Information includes basic information like the name, the file path of the datastore, or its type (IMAGE). It also includes the set of drivers (DS_MAD and TM_MAD) used to store and transfer images. In this example, the datastore uses a file-based driver (DS_MAD="fs") and the Local protocol for transfers (TM_MAD=local).
Capacity includes basic usage metrics like total, used, and free space.
Generic Attributes, under DATASTORE TEMPLATE you can find configuration attributes and custom tags (see below).
Images, the list of images currently stored in this datastore.

Note

The example above shows what a basic image datastore looks like. A Files and Kernels Datastore will look mostly the same but with different values in the type fields.

System Datastore

In the case of System Datastore the information is similar:

$ onedatastore show system
DATASTORE 0 INFORMATION
ID             : 0
NAME           : system
USER           : oneadmin
GROUP          : oneadmin
CLUSTERS       : 0
TYPE           : SYSTEM
DS_MAD         : -
TM_MAD         : local
BASE PATH      : /var/lib/one//datastores/0
DISK_TYPE      : FILE
STATE          : READY

DATASTORE CAPACITY
TOTAL:         : -
FREE:          : -
USED:          : -
LIMIT:         : -

PERMISSIONS
OWNER          : um-
GROUP          : u--
OTHER          : ---

DATASTORE TEMPLATE
ALLOW_ORPHANS="YES"
DISK_TYPE="FILE"
DS_MIGRATE="YES"
RESTRICTED_DIRS="/"
SAFE_DIRS="/var/tmp"
SHARED="NO"
TM_MAD="local"
TYPE="SYSTEM_DS"

IMAGES

Note the differences in this case:

Only the transfer driver (TM_MAD) is defined.
For the datastore of this example, there are no overall usage figures. The local driver uses the local storage area of each Host. To check the available space in a specific Host you need to check the Host details with onehost show command. Note that this behavior may be different for other drivers.
Images cannot be registered in System Datastores.

Basic Configuration

Configuring a datastore usually requires you to add some specific attributes that depend on the storage driver and your infrastructure. Check the Open Cloud Storage Guide for specific details.

Also, there are a set of common attributes that can be used in any datastore to tune its behavior. The following table describes each attribute:

Attribute	Description
`RESTRICTED_DIRS`	Paths that cannot be used to register images. A space separated list of paths.
`SAFE_DIRS`	If you need to allow a directory listed under RESTRICTED_DIRS. A space separated list of paths.
`NO_DECOMPRESS`	Do not try to untar or decompress the file to be registered. Useful for specialized Transfer Managers
`LIMIT_TRANSFER_BW`	Specify the maximum transfer rate in bytes/second when downloading images from a http/https URL. Suffixes K, M or G can be used.
`DATASTORE_CAPACITY_CHECK`	If `yes`, the available capacity of the Datastore is checked before creating a new image
`LIMIT_MB`	The maximum capacity allowed for the Datastore in `MB`. Works both ways, to reserve some Datastore capacity to be unused when `LIMIT_MB` < `TOTAL_MB` or allows Datastore overcommitment when `LIMIT_MB` > `TOTAL_MB`.
`BRIDGE_LIST`	Space separated list of hosts that have access to the storage to add new images to the datastore.
`STAGING_DIR`	Path in the storage bridge host to copy an Image before moving it to its final destination. Defaults to `/var/tmp`.
`DRIVER`	Specific image mapping driver enforcement. If present it overrides image `DRIVER` set in the image attributes and VM template.
`COMPATIBLE_SYS_DS`	Only for Image Datastores. Set the System Datastores that can be used with an Image Datastore, e.g. “0,100”
`CONTEXT_DISK_TYPE`	Specifies the disk type used for context devices (`BLOCK` or `FILE`). If not specified, `FILE` is used by default.

The Files & Kernels Datastore is a special datastore type to store plain files to be used as kernels, ram-disks, or context files. See here to learn how to define them.

Important

If you are using BRIDGE_LIST you need to install any tool needed to access the underlying storage (e.g., Ceph BRIDGE_LIST servers need Ceph client tools), as well as generic tools like qemu-img.

Disable a System Datastore

System Datastores can be disabled to prevent the scheduler from deploying new VM in them. Datastores in the disabled state are monitored as usual and the existing VM will continue to run.

$ onedatastore disable system

$ onedatastore show system
DATASTORE 0 INFORMATION
ID             : 0
NAME           : system
...
STATE          : DISABLED
...

Using Sunstone to Manage Datastores

You can also manage your Datastores using the Sunstone GUI. Select the Storage > Datastore to create, enable, disable, delete, and see information about your datastores in a user-friendly way.

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