NFS/NAS Datastore

This storage configuration assumes that your Hosts can access and mount a shared volume located on a NAS (Network Attached Storage) server. You will use this shared volume to store VM disk images files. The Virtual Machines will also boot from the shared volume.

The scalability of this solution will be bound to the performance of your NAS server. However, you can use multiple NAS servers simultaneously to improve the scalability of your OpenNebula cloud. The use of multiple NFS/NAS Datastores will allow you to:

• Balance I/O operations between storage servers.
• Apply different SLA policies (e.g., backup) to different VM types or users.
• Easily add new storage.

Using an NFS/NAS Datastore provides a straightforward solution for implementing thin provisioning for VMs, which is enabled by default when using the qcow2 image format.

Datastore setup can be done either manually or automatically:

Manual Front-end Setup

Simply mount the Image Datastore directory in the Front-end in /var/lib/one/datastores/<datastore_id>. Note that if all the Datastores are of the same type you can mount the whole /var/lib/one/datastores directory.

Manual Host Setup

The configuration is the same as for the Front-end above: simply mount in each Host the datastore directories in /var/lib/one/datastores/<datastore_id>.

Automatic Setup

Automatic NFS setup is an opt-in feature in the NFS drivers. It’s controlled via the NFS_AUTO_* family of datastore attributes documented below. If enabled, OpenNebula will lazily mount the NFS share on demand (either on Hosts or the Front-end) before an operation requires it. Also, for the transfer operations where it makes sense (for example, when deploying a VM which uses a NFS-backed system image), the mounting information is persisted to the Host’s /etc/fstab.

The unmounting/fstab cleanup is performed in a lazy way, similar to mounting. This means regular VM operations (e.g., deploy or terminate) will check whether the current machine has mounted a datastore which either has NFS_AUTO_ENABLE set to no, or does not exist anymore, and clean it up.

Other than that, the system state at the end will be similar to the way specified in the Manual Setup sections; each datastore will mount its own NFS share in /var/lib/one/datastores/<datastore_id>. In fact, there is no issue in mixing operations between datastores (i.e., managing some of them manually and some others automatically).

OpenNebula Configuration

Once Host and Front-end storage have been is set up, the OpenNebula configuration comprises the creation of the Image and System Datastores.

Create System Datastore

To create a new System Datastore, you need to set following (template) parameters:

This can be done either in Sunstone or through the CLI; for example, to create a System Datastore using the shared mode simply enter:

$ cat systemds.txt
NAME    = nfs_system
TM_MAD  = shared
TYPE    = SYSTEM_DS

$ onedatastore create systemds.txt
ID: 101

Create Image Datastore

To create a new Image Datastore, you need to set the following (template) parameters:

Configuration Attributes for NFS/NAS Datastores

For example, the following illustrates the creation of a Filesystem Datastore using the shared transfer drivers:

$ cat ds.conf
NAME   = nfs_images
DS_MAD = fs
TM_MAD = shared

$ onedatastore create ds.conf
ID: 100

Also note that there are additional attributes that can be set. Check the datastore template attributes.

Additional Configuration

• QCOW2_OPTIONS: Custom options for the qemu-img clone action. Images are created through the qemu-img command using the original image as a backing file. Custom options can be sent to qemu-img clone action through the variable QCOW2_OPTIONS in /etc/one/tmrc.
• DD_BLOCK_SIZE: Block size for dd operations (default: 64kB) can be set in /var/lib/one/remotes/etc/datastore/fs/fs.conf.
• SUPPORTED_FS: Comma-separated list with every filesystem supported for creating formatted datablocks. Can be set in /var/lib/one/remotes/etc/datastore/datastore.conf.
• FS_OPTS_<FS>: Options for creating the filesystem for formatted datablocks. Can be set in /var/lib/one/remotes/etc/datastore/datastore.conf for each filesystem type.
• SPARSE: If set to NO the images and disks in the Image and System Datastores, respectively, won’t be sparsed (i.e., the files will use all assigned space on the Datastore filesystem). It is mandatory to set QCOW2_STANDALONE = YES on the System Datastore for this setting to apply.
• QCOW2_STANDALONE: If set to YES the standalone qcow2 disk is created during CLONE operation (default: QCOW2_STANDALONE=”NO”). Unlike previous options, this one is defined in the Image Datastore template and inherited by the disks.

Attributes related to NFS auto configuration can’t be changed after datastore creation unless it is empty:

• NFS_AUTO_ENABLE: If set to YES the automatic NFS mounting functionality is enabled (default: no).
• NFS_AUTO_HOST: (Required if NFS_AUTO_ENABLE=yes) Hostname or IP address of the NFS server.
• NFS_AUTO_PATH: (Required if NFS_AUTO_ENABLE=yes) NFS share path. This share will be mounted in the hosts at the datastore path (/var/lib/one/datastores/<dsid>/).
• NFS_AUTO_OPTS: Comma-separated options (fstab-like) used for mounting the NFS shares (default: defaults).

Here’s a sample configuration for an automatically mounted image datastore:

$ cat ds.conf
NAME            = nfs_images_share1
DS_MAD          = fs
TM_MAD          = shared
NFS_AUTO_ENABLE = yes
NFS_AUTO_HOST   = 192.168.150.10
NFS_AUTO_PATH   = /srv/share1
NFS_AUTO_OPTS   = "soft,intr,rsize=32768,wsize=32768"

$ onedatastore create ds.conf
ID: 102

NFS/NAS and Local Storage

When using the NFS/NAS Datastore, you can improve VM performance by placing the disks in the Host’s local storage area. In this way, you will have a repository of images (distributed across the Hosts using a shared FS) but the VMs running from the local disks. This effectively combines NFS/NAS and Local Storage datastores.

To configure this scenario, simply configure a shared Image and System Datastores as described above (TM_MAD=shared). Then, add a Local Storage System Datastore (TM_MAD=ssh). Any image registered in the Image Datastore can now be deployed using any of these Datastores.

To select the (alternate) deployment mode, add the following attribute to the Virtual Machine template:

• TM_MAD_SYSTEM="ssh"

Datastore Internals

Images are saved into the corresponding datastore directory (/var/lib/one/datastores/<DATASTORE ID>). Also, for each running Virtual Machine there is a directory (named after the VM ID) in the corresponding System Datastore. These directories contain the VM disks and additional files, e.g., checkpoint or snapshots.

For example, a system with an Image Datastore (1) with three images and three Virtual Machines (VM 0 and 2 running, and VM 7 stopped) running from System Datastore 0 would present the following layout:

/var/lib/one/datastores
|-- 0/
|   |-- 0/
|   |   |-- disk.0
|   |   `-- disk.1
|   |-- 2/
|   |   `-- disk.0
|   `-- 7/
|       |-- checkpoint
|       `-- disk.0
`-- 1
    |-- 05a38ae85311b9dbb4eb15a2010f11ce
    |-- 2bbec245b382fd833be35b0b0683ed09
    `-- d0e0df1fb8cfa88311ea54dfbcfc4b0c

The shared transfer driver assumes that the datastore is mounted on all the Hosts (Front-end and Hosts) of the cluster. Typically this is achieved through a shared filesystem, e.g., NFS, GlusterFS, or Lustre. This transfer mode usually reduces VM deployment times, but it can also become a bottleneck in your infrastructure and degrade your Virtual Machines’ performance if the virtualized services perform disk-intensive workloads. Usually, this limitation may be overcome by:

• Using different filesystem servers for the Image Datastores so the actual I/O bandwidth is balanced.
• Using the Host local storage.
• Tuning or improving the filesystem servers.

When a VM is created, its disks (the disk.i files) are copied or linked in the corresponding directory of the System Datastore. These file operations are always performed remotely on the target Host.

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