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Virtualization Guide / Managing virtual machines with libvirt / Preparing the VM Host Server
Applies to openSUSE Leap 15.4

8 Preparing the VM Host Server

  

Before you can install guest virtual machines, you need to prepare the VM Host Server to provide the guests with the resources that they need for their operation. Specifically, you need to configure:

  • Networking so that guests can make use of the network connection provided the host.

  • A storage pool reachable from the host so that the guests can store their disk images.

8.1 Configuring networks

  

There are two common network configurations to provide a VM Guest with a network connection:

  • A network bridge. This is the default and recommended way of providing the guests with network connection.

  • A virtual network with forwarding enabled.

8.1.1 Network bridge

  

The network bridge configuration provides a Layer 2 switch for VM Guests, switching Layer 2 Ethernet packets between ports on the bridge based on MAC addresses associated with the ports. This gives the VM Guest Layer 2 access to the VM Host Server's network. This configuration is analogous to connecting the VM Guest's virtual Ethernet cable into a hub that is shared with the host and other VM Guests running on the host. The configuration is often referred to as shared physical device.

The network bridge configuration is the default configuration of openSUSE Leap when configured as a KVM or Xen hypervisor. It is the preferred configuration when you simply want to connect VM Guests to the VM Host Server's LAN.

Which tool to use to create the network bridge depends on the service you use to manage the network connection on the VM Host Server:

  • If a network connection is managed by wicked, use either YaST or the command line to create the network bridge. wicked is the default on server hosts.

  • If a network connection is managed by NetworkManager, use the NetworkManager command line tool nmcli to create the network bridge. NetworkManager is the default on desktop and laptops.

8.1.1.1 Managing network bridges with YaST

  

This section includes procedures to add or remove network bridges with YaST.

8.1.1.1.1 Adding a network bridge
  

To add a network bridge on VM Host Server, follow these steps:

  1. Start YaST › System › Network Settings.

  2. Activate the Overview tab and click Add.

  3. Select Bridge from the Device Type list and enter the bridge device interface name in the Configuration Name entry. Click the Next button to proceed.

  4. In the Address tab, specify networking details such as DHCP/static IP address, subnet mask or host name.

    Using Dynamic Address is only useful when also assigning a device to a bridge that is connected to a DHCP server.

    If you intend to create a virtual bridge that has no connection to a real network device, use Statically assigned IP Address. In this case, it is a good idea to use addresses from the private IP address ranges, for example, 192.168.0.0/16, 172.16.0.0/12, or 10.0.0.0/8.

    To create a bridge that should only serve as a connection between the different guests without connection to the host system, set the IP address to 0.0.0.0 and the subnet mask to 255.255.255.255. The network scripts handle this special address as an unset IP address.

  5. Activate the Bridged Devices tab and activate the network devices you want to include in the network bridge.

  6. Click Next to return to the Overview tab and confirm with OK. The new network bridge should now be active on VM Host Server.

8.1.1.1.2 Deleting a network bridge
  

To delete an existing network bridge, follow these steps:

  1. Start YaST › System › Network Settings.

  2. Select the bridge device you want to delete from the list in the Overview tab.

  3. Delete the bridge with Delete and confirm with OK.

8.1.1.2 Managing network bridges from the command line

  

This section includes procedures to add or remove network bridges using the command line.

8.1.1.2.1 Adding a network bridge
  

To add a new network bridge device on VM Host Server, follow these steps:

  1. Log in as root on the VM Host Server where you want to create a new network bridge.

  2. Choose a name for the new bridge—virbr_test in our example—and run 

    # ip link add name VIRBR_TEST type bridge

  3. Check if the bridge was created on VM Host Server: 

    # bridge vlan
[...]
virbr_test  1 PVID Egress Untagged

    virbr_test is present, but is not associated with any physical network interface.

  4. Bring the network bridge up and add a network interface to the bridge: 

    # ip link set virbr_test up
# ip link set eth1 master virbr_test
    Important
    Important: Network interface must be unused

    You can only assign a network interface that is not yet used by another network bridge.

  5. Optionally, enable STP (see Spanning Tree Protocol): 

    # bridge link set dev virbr_test cost 4
8.1.1.2.2 Deleting a network bridge
  

To delete an existing network bridge device on VM Host Server from the command line, follow these steps:

  1. Log in as root on the VM Host Server where you want to delete an existing network bridge.

  2. List existing network bridges to identify the name of the bridge to remove: 

    # bridge vlan
[...]
virbr_test  1 PVID Egress Untagged

  3. Delete the bridge: 

    # ip link delete dev virbr_test

8.1.1.3 Adding a network bridge with nmcli

  

This section includes procedures to add a network bridge with NetworkManager's command line tool nmcli.

  1. List active network connections: 

    > sudo nmcli connection show --active
NAME                   UUID                                  TYPE      DEVICE
Ethernet connection 1  84ba4c22-0cfe-46b6-87bb-909be6cb1214  ethernet  eth0

  2. Add a new bridge device named br0 and verify its creation: 

    > sudo nmcli connection add type bridge ifname br0
Connection 'bridge-br0' (36e11b95-8d5d-4a8f-9ca3-ff4180eb89f7) \
successfully added.
> sudo nmcli connection show --active
NAME                   UUID                                  TYPE      DEVICE
bridge-br0             36e11b95-8d5d-4a8f-9ca3-ff4180eb89f7  bridge    br0
Ethernet connection 1  84ba4c22-0cfe-46b6-87bb-909be6cb1214  ethernet  eth0

  3. Optionally, you can view the bridge settings: 

    > sudo nmcli -f bridge connection show bridge-br0
bridge.mac-address:                     --
bridge.stp:                             yes
bridge.priority:                        32768
bridge.forward-delay:                   15
bridge.hello-time:                      2
bridge.max-age:                         20
bridge.ageing-time:                     300
bridge.group-forward-mask:              0
bridge.multicast-snooping:              yes
bridge.vlan-filtering:                  no
bridge.vlan-default-pvid:               1
bridge.vlans:                           --

  4. Link the bridge device to the physical Ethernet device eth0: 

    > sudo nmcli connection add type bridge-slave ifname eth0 master br0

  5. Disable the eth0 interface and enable the new bridge: 

    > sudo nmcli connection down "Ethernet connection 1"
> sudo nmcli connection up bridge-br0
Connection successfully activated (master waiting for slaves) \
(D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/9)

8.1.1.4 Using VLAN interfaces

  

Sometimes it is necessary to create a private connection either between two VM Host Servers or between VM Guest systems. For example, to migrate a VM Guest to hosts in a different network segment. Or to create a private bridge that only VM Guest systems may connect to (even when running on different VM Host Server systems). An easy way to build such connections is to set up VLAN networks.

VLAN interfaces are commonly set up on the VM Host Server. They either interconnect the different VM Host Server systems, or they may be set up as a physical interface to an otherwise virtual-only bridge. It is even possible to create a bridge with a VLAN as a physical interface that has no IP address in the VM Host Server. That way, the guest systems have no possibility to access the host over this network.

Run the YaST module System › Network Settings. Follow this procedure to set up the VLAN device:

Procedure 8.1: Setting up VLAN interfaces with YaST
  

  1. Click Add to create a new network interface.

  2. In the Hardware Dialog, select Device Type VLAN.

  3. Change the value of Configuration Name to the ID of your VLAN. Note that VLAN ID 1 is commonly used for management purposes.

  4. Click Next.

  5. Select the interface that the VLAN device should connect to below Real Interface for VLAN. If the desired interface does not appear in the list, first set up this interface without an IP address.

  6. Select the desired method for assigning an IP address to the VLAN device.

  7. Click Next to finish the configuration.

It is also possible to use the VLAN interface as a physical interface of a bridge. This makes it possible to connect several VM Host Server-only networks and allows live migration of VM Guest systems that are connected to such a network.

YaST does not always allow setting no IP address. However, this may be a desired feature, especially if VM Host Server-only networks should be connected. In this case, use the special address 0.0.0.0 with netmask 255.255.255.255. The system scripts handle this address as no IP address set.

8.1.2 Virtual networks

  

libvirt-managed virtual networks are similar to bridged networks, but typically have no Layer 2 connection to the VM Host Server. Connectivity to the VM Host Server's physical network is accomplished with Layer 3 forwarding, which introduces additional packet processing on the VM Host Server as compared to a Layer 2 bridged network. Virtual networks also provide DHCP and DNS services for VM Guests. For more information on libvirt virtual networks, see the Network XML format documentation at https://libvirt.org/formatnetwork.html.

A standard libvirt installation on openSUSE Leap already comes with a predefined virtual network named default. It provides DHCP and DNS services for the network, along with connectivity to the VM Host Server's physical network using the network address translation (NAT) forwarding mode. Although it is predefined, the default virtual network needs to be explicitly enabled by the administrator. For more information on the forwarding modes supported by libvirt, see the Connectivity section of the Network XML format documentation at https://libvirt.org/formatnetwork.html#elementsConnect.

libvirt-managed virtual networks can be used to satisfy a wide range of use cases, but are commonly used on VM Host Servers that have a wireless connection or dynamic/sporadic network connectivity, such as laptops. Virtual networks are also useful when the VM Host Server's network has limited IP addresses, allowing forwarding of packets between the virtual network and the VM Host Server's network. However, most server use cases are better suited for the network bridge configuration, where VM Guests are connected to the VM Host Server's LAN.

Warning
Warning: Enabling forwarding mode

Enabling forwarding mode in a libvirt virtual network enables forwarding in the VM Host Server by setting /proc/sys/net/ipv4/ip_forward and /proc/sys/net/ipv6/conf/all/forwarding to 1, which essentially turns the VM Host Server into a router. Restarting the VM Host Server's network may reset the values and disable forwarding. To avoid this behavior, explicitly enable forwarding in the VM Host Server by editing the /etc/sysctl.conf file and adding: 

net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1

8.1.2.1 Managing virtual networks with Virtual Machine Manager

  

You can define, configure, and operate virtual networks with Virtual Machine Manager.

8.1.2.1.1 Defining virtual networks
  

  1. Start Virtual Machine Manager. In the list of available connections, right-click the name of the connection for which you need to configure the virtual network, and then select Details.

  2. In the Connection Details window, click the Virtual Networks tab. You can see the list of all virtual networks available for the current connection. On the right, there are details of the selected virtual network.

    Connection details
    Figure 8.1: Connection details
      

  3. To add a new virtual network, click Add.

  4. Specify a name for the new virtual network.

    Create virtual network
    Figure 8.2: Create virtual network
      

  5. Specify the networking mode. For the NAT and Routed types, you can specify to which device to forward network communications. While NAT (network address translation) remaps the virtual network address space and allows sharing a single IP address, Routed forwards packets from the virtual network to the VM Host Server's physical network with no translation.

  6. If you need IPv4 networking, activate Enable IPv4 and specify the IPv4 network address. If you need a DHCP server, activate Enable DHCPv4 and specify the assignable IP address range.

  7. If you need IPv6 networking, activate Enable IPv6 and specify the IPv6 network address. If you need a DHCP server, activate Enable DHCPv6 and specify the assignable IP address range.

  8. If you want to specify a different domain name than the name of the virtual network, select Custom under DNS domain name and enter it here.

  9. Click Finish to create the new virtual network. On the VM Host Server, a new virtual network bridge virbrX is available, which corresponds to the newly created virtual network. You can check with bridge link. libvirt automatically adds iptables rules to allow traffic to/from guests attached to the new virbrX device.

8.1.2.1.2 Starting virtual networks
  

To start a virtual network that is temporarily stopped, follow these steps:

  1. Start Virtual Machine Manager. In the list of available connections, right-click the name of the connection for which you need to configure the virtual network, and then select Details.

  2. In the Connection Details window, click the Virtual Networks tab. You can see the list of all virtual networks available for the current connection.

  3. To start the virtual network, click Start.

8.1.2.1.3 Stopping virtual networks
  

To stop an active virtual network, follow these steps:

  1. Start Virtual Machine Manager. In the list of available connections, right-click the name of the connection for which you need to configure the virtual network, and then select Details.

  2. In the Connection Details window, click the Virtual Networks tab. You can see the list of all virtual networks available for the current connection.

  3. Select the virtual network to be stopped, then click Stop.

8.1.2.1.4 Deleting virtual networks
  

To delete a virtual network from VM Host Server, follow these steps:

  1. Start Virtual Machine Manager. In the list of available connections, right-click the name of the connection for which you need to configure the virtual network, and then select Details.

  2. In the Connection Details window, click the Virtual Networks tab. You can see the list of all virtual networks available for the current connection.

  3. Select the virtual network to be deleted, then click Delete.

8.1.2.1.5 Obtaining IP addresses with nsswitch for NAT networks (in KVM)
  

  • On VM Host Server, install libvirt-nss, which provides NSS support for libvirt: 

    > sudo zypper in libvirt-nss

  • Add libvirt to /etc/nsswitch.conf: 

    ...
hosts:  files libvirt mdns_minimal [NOTFOUND=return] dns
...

  • If NSCD is running, restart it: 

    > sudo systemctl restart nscd

Now you can reach the guest system by name from the host.

The NSS module has limited functionality. It reads /var/lib/libvirt/dnsmasq/*.status files to find the host name and corresponding IP addresses in a JSON record describing each lease provided by dnsmasq. Host name translation can only be done on those VM Host Servers using a libvirt-managed bridged network backed by dnsmasq.

8.1.2.2 Managing virtual networks with virsh

  

You can manage libvirt-provided virtual networks with the virsh command line tool. To view all network related virsh commands, run 

> sudo virsh help network
Networking (help keyword 'network'):
 net-autostart                  autostart a network
        net-create                     create a network from an XML file
        net-define                     define (but don't start) a network from an XML file
        net-destroy                    destroy (stop) a network
        net-dumpxml                    network information in XML
        net-edit                       edit XML configuration for a network
        net-event                      Network Events
        net-info                       network information
        net-list                       list networks
        net-name                       convert a network UUID to network name
        net-start                      start a (previously defined) inactive network
        net-undefine                   undefine an inactive network
        net-update                     update parts of an existing network's configuration
 net-uuid                       convert a network name to network UUID

To view brief help information for a specific virsh command, run virsh help VIRSH_COMMAND: 

> sudo virsh help net-create
  NAME
    net-create - create a network from an XML file

  SYNOPSIS
    net-create <file>

  DESCRIPTION
    Create a network.

  OPTIONS
    [--file] <string>  file containing an XML network description
8.1.2.2.1 Creating a network
  

To create a new running virtual network, run 

> sudo virsh net-create VNET_DEFINITION.xml

The VNET_DEFINITION.xml XML file includes the definition of the virtual network that libvirt accepts.

To define a new virtual network without activating it, run 

> sudo virsh net-define VNET_DEFINITION.xml

The following examples illustrate definitions of different types of virtual networks.

Example 8.1: NAT-based network
  

The following configuration allows VM Guests outgoing connectivity if it is available on the VM Host Server. In the absence of VM Host Server networking, it allows guests to talk directly to each other. 

<network>
<name>vnet_nated</name>1
<bridge name="virbr1"/>2
 <forward mode="nat"/>3
 <ip address="192.168.122.1" netmask="255.255.255.0">4
  <dhcp>
   <range start="192.168.122.2" end="192.168.122.254"/>5
   <host mac="52:54:00:c7:92:da" name="host1.testing.com" \
    ip="192.168.1.101"/>6
   <host mac="52:54:00:c7:92:db" name="host2.testing.com" \
    ip="192.168.1.102"/>
   <host mac="52:54:00:c7:92:dc" name="host3.testing.com" \
    ip="192.168.1.103"/>
  </dhcp>
 </ip>
</network>

1

The name of the new virtual network.

2

The name of the bridge device used to construct the virtual network. When defining a new network with a <forward> mode of "nat" or "route" (or an isolated network with no <forward> element), libvirt will automatically generate a unique name for the bridge device if none is given.

3

Inclusion of the <forward> element indicates that the virtual network will be connected to the physical LAN. The mode attribute specifies the forwarding method. The most common modes are "nat" (Network Address Translation, the default), "route" (direct forwarding to the physical network, no address translation), and "bridge" (network bridge configured outside of libvirt). If the <forward> element is not specified, the virtual network will be isolated from other networks. For a complete list of forwarding modes, see https://libvirt.org/formatnetwork.html#elementsConnect.

4

The IP address and netmask for the network bridge.

5

Enable DHCP server for the virtual network, offering IP addresses ranging from the specified start and end attributes.

6

The optional <host> elements specify hosts that will be given names and predefined IP addresses by the built-in DHCP server. Any IPv4 host element must specify the following: the MAC address of the host to be assigned a given name, the IP to be assigned to that host, and the name to be given to that host by the DHCP server. An IPv6 host element differs slightly from that for IPv4: there is no mac attribute since a MAC address has no defined meaning in IPv6. Instead, the name attribute is used to identify the host to be assigned the IPv6 address. For DHCPv6, the name is the plain name of the client host sent by the client to the server. Note that this method of assigning a specific IP address can also be used instead of the mac attribute for IPv4.

Example 8.2: Routed network
  

The following configuration routes traffic from the virtual network to the LAN without applying any NAT. The IP address range must be preconfigured in the routing tables of the router on the VM Host Server network. 

<network>
 <name>vnet_routed</name>
 <bridge name="virbr1"/>
 <forward mode="route" dev="eth1"/>1
 <ip address="192.168.122.1" netmask="255.255.255.0">
  <dhcp>
   <range start="192.168.122.2" end="192.168.122.254"/>
  </dhcp>
 </ip>
</network>

1

The guest traffic may only go out via the eth1 network device on the VM Host Server.

Example 8.3: Isolated network
  

This configuration provides a completely isolated private network. The guests can talk to each other, and to VM Host Server, but cannot reach any other machines on the LAN, as the <forward> element is missing in the XML description. 

<network>
 <name>vnet_isolated</name>
 <bridge name="virbr3"/>
 <ip address="192.168.152.1" netmask="255.255.255.0">
  <dhcp>
   <range start="192.168.152.2" end="192.168.152.254"/>
  </dhcp>
 </ip>
 </network>
Example 8.4: Using an existing bridge on VM Host Server
  

This configuration shows how to use an existing VM Host Server's network bridge br0. VM Guests are directly connected to the physical network. Their IP addresses will all be on the subnet of the physical network, and there will be no restrictions on incoming or outgoing connections. 

<network>
        <name>host-bridge</name>
        <forward mode="bridge"/>
        <bridge name="br0"/>
</network>
8.1.2.2.2 Listing networks
  

To list all virtual networks available to libvirt, run: 

> sudo virsh net-list --all

 Name                 State      Autostart     Persistent
----------------------------------------------------------
 crowbar              active     yes           yes
 vnet_nated           active     yes           yes
 vnet_routed          active     yes           yes
 vnet_isolated        inactive   yes           yes

To list available domains, run: 

> sudo virsh list
 Id    Name                           State
----------------------------------------------------
 1     nated_sles12sp3                running
 ...

To get a list of interfaces of a running domain, run domifaddr DOMAIN, or optionally specify the interface to limit the output to this interface. By default, it additionally outputs their IP and MAC addresses: 

> sudo virsh domifaddr nated_sles12sp3 --interface vnet0 --source lease
 Name       MAC address          Protocol     Address
-------------------------------------------------------------------------------
 vnet0      52:54:00:9e:0d:2b    ipv6         fd00:dead:beef:55::140/64
 -          -                    ipv4         192.168.100.168/24

To print brief information of all virtual interfaces associated with the specified domain, run: 

> sudo virsh domiflist nated_sles12sp3
Interface  Type       Source       Model       MAC
---------------------------------------------------------
vnet0      network    vnet_nated   virtio      52:54:00:9e:0d:2b
8.1.2.2.3 Getting details about a network
  

To get detailed information about a network, run: 

> sudo virsh net-info vnet_routed
Name:           vnet_routed
UUID:           756b48ff-d0c6-4c0a-804c-86c4c832a498
Active:         yes
Persistent:     yes
Autostart:      yes
Bridge:         virbr5
8.1.2.2.4 Starting a network
  

To start an inactive network that was already defined, find its name (or unique identifier, UUID) with: 

> sudo virsh net-list --inactive
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 vnet_isolated        inactive   yes           yes

Then run: 

> sudo virsh net-start vnet_isolated
Network vnet_isolated started
8.1.2.2.5 Stopping a network
  

To stop an active network, find its name (or unique identifier, UUID) with: 

> sudo virsh net-list --inactive
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 vnet_isolated        active     yes           yes

Then run: 

> sudo virsh net-destroy vnet_isolated
Network vnet_isolated destroyed
8.1.2.2.6 Removing a network
  

To remove the definition of an inactive network from VM Host Server permanently, run: 

> sudo virsh net-undefine vnet_isolated
Network vnet_isolated has been undefined

8.2 Configuring a storage pool

  

When managing a VM Guest on the VM Host Server itself, you can access the complete file system of the VM Host Server to attach or create virtual hard disks or to attach existing images to the VM Guest. However, this is not possible when managing VM Guests from a remote host. For this reason, libvirt supports so called “Storage Pools”, which can be accessed from remote machines.

Tip
Tip: CD/DVD ISO images

To be able to access CD/DVD ISO images on the VM Host Server from remote clients, they also need to be placed in a storage pool.

libvirt knows two different types of storage: volumes and pools.

Storage volume

A storage volume is a storage device that can be assigned to a guest—a virtual disk or a CD/DVD/floppy image. Physically, it can be a block device—for example, a partition or a logical volume—or a file on the VM Host Server.

Storage pool

A storage pool is a storage resource on the VM Host Server that can be used for storing volumes, similar to network storage for a desktop machine. Physically it can be one of the following types:

File system directory (dir)

A directory for hosting image files. The files can be either one of the supported disk formats (raw or qcow2), or ISO images.

Physical disk device (disk)

Use a complete physical disk as storage. A partition is created for each volume that is added to the pool.

Pre-formatted block device (fs)

Specify a partition to be used in the same way as a file system directory pool (a directory for hosting image files). The only difference to using a file system directory is that libvirt takes care of mounting the device.

iSCSI target (iscsi)

Set up a pool on an iSCSI target. You need to have been logged in to the volume once before to use it with libvirt. Use the YaST iSCSI Initiator to detect and log in to a volume. Volume creation on iSCSI pools is not supported; instead, each existing Logical Unit Number (LUN) represents a volume. Each volume/LUN also needs a valid (empty) partition table or disk label before you can use it. If missing, use fdisk to add it: 

> sudo fdisk -cu /dev/disk/by-path/ip-192.168.2.100:3260-iscsi-iqn.2010-10.com.example:[...]-lun-2
Device contains neither a valid DOS partition table, nor Sun, SGI
or OSF disklabel
Building a new DOS disklabel with disk identifier 0xc15cdc4e.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
LVM volume group (logical)

Use an LVM volume group as a pool. You can either use a predefined volume group, or create a group by specifying the devices to use. Storage volumes are created as partitions on the volume.

Warning
Warning: Deleting the LVM-based pool

When the LVM-based pool is deleted in the Storage Manager, the volume group is deleted as well. This results in a non-recoverable loss of all data stored on the pool!

Multipath devices (mpath)

At the moment, multipathing support is limited to assigning existing devices to the guests. Volume creation or configuring multipathing from within libvirt is not supported.

Network exported directory (netfs)

Specify a network directory to be used in the same way as a file system directory pool (a directory for hosting image files). The only difference to using a file system directory is that libvirt takes care of mounting the directory. The supported protocol is NFS.

SCSI host adapter (scsi)

Use an SCSI host adapter in almost the same way as an iSCSI target. We recommend to use a device name from /dev/disk/by-* rather than /dev/sdX. The latter can change (for example, when adding or removing hard disks). Volume creation on iSCSI pools is not supported. Instead, each existing LUN (Logical Unit Number) represents a volume.

Warning
Warning: Security considerations

To avoid data loss or data corruption, do not attempt to use resources such as LVM volume groups, iSCSI targets, etc., that are also used to build storage pools on the VM Host Server. There is no need to connect to these resources from the VM Host Server or to mount them on the VM Host Server—libvirt takes care of this.

Do not mount partitions on the VM Host Server by label. Under certain circumstances it is possible that a partition is labeled from within a VM Guest with a name already existing on the VM Host Server.

8.2.1 Managing storage with virsh

  

Managing storage from the command line is also possible by using virsh. However, creating storage pools is currently not supported by SUSE. Therefore, this section is restricted to documenting functions such as starting, stopping, and deleting pools, and volume management.

A list of all virsh subcommands for managing pools and volumes is available by running virsh help pool and virsh help volume, respectively.

8.2.1.1 Listing pools and volumes

  

List all pools currently active by executing the following command. To also list inactive pools, add the option --all: 

> virsh pool-list --details

Details about a specific pool can be obtained with the pool-info subcommand: 

> virsh pool-info POOL

By default, volumes can only be listed per pool. To list all volumes from a pool, enter the following command. 

> virsh vol-list --details POOL

At the moment virsh offers no tools to show whether a volume is used by a guest or not. The following procedure describes a way to list volumes from all pools that are currently used by a VM Guest.

Procedure 8.2: Listing all storage volumes currently used on a VM Host Server
  

  1. Create an XSLT style sheet by saving the following content to a file, for example, ~/libvirt/guest_storage_list.xsl: 

    <?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>
  <xsl:template match="text()"/>
  <xsl:strip-space elements="*"/>
  <xsl:template match="disk">
    <xsl:text>  </xsl:text>
    <xsl:value-of select="(source/@file|source/@dev|source/@dir)[1]"/>
    <xsl:text>&#10;</xsl:text>
  </xsl:template>
</xsl:stylesheet>

  2. Run the following commands in a shell. It is assumed that the guest's XML definitions are all stored in the default location (/etc/libvirt/qemu). xsltproc is provided by the package libxslt. 

    SSHEET="$HOME/libvirt/guest_storage_list.xsl"
cd /etc/libvirt/qemu
for FILE in *.xml; do
  basename $FILE .xml
  xsltproc $SSHEET $FILE
done

8.2.1.2 Starting, stopping, and deleting pools

  

Use the virsh pool subcommands to start, stop, or delete a pool. Replace POOL with the pool's name or its UUID in the following examples:

Stopping a pool
> virsh pool-destroy POOL
Note
Note: A pool's state does not affect attached volumes

Volumes from a pool attached to VM Guests are always available, regardless of the pool's state (Active (stopped) or Inactive (started)). The state of the pool solely affects the ability to attach volumes to a VM Guest via remote management.

Deleting a pool
> virsh pool-delete POOL
Warning
Warning: Deleting storage pools

See Warning: Deleting storage pools

Starting a pool
> virsh pool-start POOL
Enable autostarting a pool
> virsh pool-autostart POOL

Only pools that are marked to autostart will automatically be started if the VM Host Server reboots.

Disable autostarting a pool
> virsh pool-autostart POOL --disable

8.2.1.3 Adding volumes to a storage pool

  

virsh offers two ways to add volumes to storage pools: either from an XML definition with vol-create and vol-create-from or via command line arguments with vol-create-as. The first two methods are currently not supported by SUSE, therefore this section focuses on the subcommand vol-create-as.

To add a volume to an existing pool, enter the following command: 

> virsh vol-create-as POOL1NAME2 12G --format3raw|qcow24 --allocation 4G5

1

Name of the pool to which the volume should be added

2

Name of the volume

3

Size of the image, in this example 12 gigabytes. Use the suffixes k, M, G, T for kilobyte, megabyte, gigabyte, and terabyte, respectively.

4

Format of the volume. SUSE currently supports raw and qcow2.

5

Optional parameter. By default, virsh creates a sparse image file that grows on demand. Specify the amount of space that should be allocated with this parameter (4 gigabytes in this example). Use the suffixes k, M, G, T for kilobyte, megabyte, gigabyte, and terabyte, respectively.

When not specifying this parameter, a sparse image file with no allocation will be generated. To create a non-sparse volume, specify the whole image size with this parameter (would be 12G in this example).

8.2.1.3.1 Cloning existing volumes
  

Another way to add volumes to a pool is to clone an existing volume. The new instance is always created in the same pool as the original. 

> virsh vol-clone NAME_EXISTING_VOLUME1NAME_NEW_VOLUME2 --pool POOL3

1

Name of the existing volume that should be cloned

2

Name of the new volume

3

Optional parameter. libvirt tries to locate the existing volume automatically. If that fails, specify this parameter.

8.2.1.4 Deleting volumes from a storage pool

  

To permanently delete a volume from a pool, use the subcommand vol-delete: 

> virsh vol-delete NAME --pool POOL

--pool is optional. libvirt tries to locate the volume automatically. If that fails, specify this parameter.

Warning
Warning: No checks upon volume deletion

A volume will be deleted in any case, regardless of whether it is currently used in an active or inactive VM Guest. There is no way to recover a deleted volume.

Whether a volume is used by a VM Guest can only be detected by using by the method described in Procedure 8.2, “Listing all storage volumes currently used on a VM Host Server”.

8.2.1.5 Attaching volumes to a VM Guest

  

After you create a volume as described in Section 8.2.1.3, “Adding volumes to a storage pool”, you can attach it to a virtual machine and use it as a hard disk: 

> virsh attach-disk DOMAIN SOURCE_IMAGE_FILE TARGET_DISK_DEVICE

For example: 

> virsh attach-disk sles12sp3 /virt/images/example_disk.qcow2 sda2

To check if the new disk is attached, inspect the result of the virsh dumpxml command: 

# virsh dumpxml sles12sp3
[...]
<disk type='file' device='disk'>
 <driver name='qemu' type='raw'/>
 <source file='/virt/images/example_disk.qcow2'/>
 <backingStore/>
 <target dev='sda2' bus='scsi'/>
 <alias name='scsi0-0-0'/>
 <address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>
[...]
8.2.1.5.1 Hotplug or persistent change
  

You can attach disks to both active and inactive domains. The attachment is controlled by the --live and --config options:

--live

Hotplugs the disk to an active domain. The attachment is not saved in the domain configuration. Using --live on an inactive domain is an error.

--config

Changes the domain configuration persistently. The attached disk is then available after the next domain start.

--live--config

Hotplugs the disk and adds it to the persistent domain configuration.

Tip
Tip: virsh attach-device

virsh attach-device is the more generic form of virsh attach-disk. You can use it to attach other types of devices to a domain.

8.2.1.6 Detaching volumes from a VM Guest

  

To detach a disk from a domain, use virsh detach-disk: 

# virsh detach-disk DOMAIN TARGET_DISK_DEVICE

For example: 

# virsh detach-disk sles12sp3 sda2

You can control the attachment with the --live and --config options as described in Section 8.2.1.5, “Attaching volumes to a VM Guest”.

8.2.2 Managing storage with Virtual Machine Manager

  

The Virtual Machine Manager provides a graphical interface—the Storage Manager—to manage storage volumes and pools. To access it, either right-click a connection and choose Details, or highlight a connection and choose Edit › Connection Details. Select the Storage tab.

Image

8.2.2.1 Adding a storage pool

  

To add a storage pool, proceed as follows:

  1. Click Add in the bottom left corner. The dialog Add a New Storage Pool appears.

  2. Provide a Name for the pool (consisting of only alphanumeric characters and _, - or .) and select a Type.

    Image

  3. Specify the required details below. They depend on the type of pool you are creating.

    Important
    Important

    ZFS pools are not supported.

    Type dir

    • Target Path: Specify an existing directory.

    Type disk

    • Format: Format of the device's partition table. Using auto should usually work. If not, get the required format by running the command parted -l on the VM Host Server.

    • Source Path: Path to the device. It is recommended to use a device name from /dev/disk/by-* rather than the simple /dev/sdX, since the latter can change (for example, when adding or removing hard disks). You need to specify the path that resembles the whole disk, not a partition on the disk (if existing).

    Type fs

    • Target Path: Mount point on the VM Host Server file system.

    • Format: File system format of the device. The default value auto should work.

    • Source Path: Path to the device file. It is recommended to use a device name from /dev/disk/by-* rather than /dev/sdX, because the latter can change (for example, when adding or removing hard disks).

    Type iscsi

    Get the necessary data by running the following command on the VM Host Server: 

    > sudo iscsiadm --mode node

    It will return a list of iSCSI volumes with the following format. The elements in bold text are required: 

    IP_ADDRESS:PORT,TPGT TARGET_NAME_(IQN)

    • Target Path: The directory containing the device file. Use /dev/disk/by-path (default) or /dev/disk/by-id.

    • Host Name: Host name or IP address of the iSCSI server.

    • Source IQN: The iSCSI target name (iSCSI Qualified Name).

    • Initiator IQN: The iSCSI initiator name.

    Type logical

    • Volgroup Name: Specify the device path of an existing volume group.

    Type mpath

    • Target Path: Support for multipathing is currently limited to making all multipath devices available. Therefore, specify an arbitrary string here that will then be ignored. The path is required, otherwise the XML parser will fail.

    Type netfs

    • Target Path: Mount point on the VM Host Server file system.

    • Host Name: IP address or host name of the server exporting the network file system.

    • Source Path: Directory on the server that is being exported.

    Type rbd

    • Host Name: Host name of the server with an exported RADOS block device.

    • Source Name: Name of the RADOS block device on the server.

    Type scsi

    • Target Path: The directory containing the device file. Use /dev/disk/by-path (default) or /dev/disk/by-id.

    • Source Path: Name of the SCSI adapter.

    Note
    Note: File browsing

    Using the file browser by clicking Browse is not possible when operating remotely.

  4. Click Finish to add the storage pool.

8.2.2.2 Managing storage pools

  

Virtual Machine Manager's Storage Manager lets you create or delete volumes in a pool. You may also temporarily deactivate or permanently delete existing storage pools. Changing the basic configuration of a pool is currently not supported by SUSE.

8.2.2.2.1 Starting, stopping, and deleting pools
  

The purpose of storage pools is to provide block devices located on the VM Host Server that can be added to a VM Guest when managing it from remote. To make a pool temporarily inaccessible from remote, click Stop in the bottom left corner of the Storage Manager. Stopped pools are marked with State: Inactive and are grayed out in the list pane. By default, a newly created pool will be automatically started On Boot of the VM Host Server.

To start an inactive pool and make it available from remote again, click Start in the bottom left corner of the Storage Manager.

Note
Note: A pool's state does not affect attached volumes

Volumes from a pool attached to VM Guests are always available, regardless of the pool's state (Active (stopped) or Inactive (started)). The state of the pool solely affects the ability to attach volumes to a VM Guest via remote management.

To permanently make a pool inaccessible, click Delete in the bottom left corner of the Storage Manager. You can only delete inactive pools. Deleting a pool does not physically erase its contents on VM Host Server—it only deletes the pool configuration. However, you need to be extra careful when deleting pools, especially when deleting LVM volume group-based tools:

Warning
Warning: Deleting storage pools

Deleting storage pools based on local file system directories, local partitions or disks has no effect on the availability of volumes from these pools currently attached to VM Guests.

Volumes located in pools of type iSCSI, SCSI, LVM group or Network Exported Directory will become inaccessible from the VM Guest if the pool is deleted. Although the volumes themselves will not be deleted, the VM Host Server will no longer have access to the resources.

Volumes on iSCSI/SCSI targets or Network Exported Directory will become accessible again when creating an adequate new pool or when mounting/accessing these resources directly from the host system.

When deleting an LVM group-based storage pool, the LVM group definition will be erased and the LVM group will no longer exist on the host system. The configuration is not recoverable and all volumes from this pool are lost.

8.2.2.2.2 Adding volumes to a storage pool
  

Virtual Machine Manager lets you create volumes in all storage pools, except in pools of types Multipath, iSCSI, or SCSI. A volume in these pools is equivalent to a LUN and cannot be changed from within libvirt.

  1. A new volume can either be created using the Storage Manager or while adding a new storage device to a VM Guest. In either case, select a storage pool from the left panel, then click Create new volume.

  2. Specify a Name for the image and choose an image format.

    SUSE currently only supports raw or qcow2 images. The latter option is not available on LVM group-based pools.

    Next to Max Capacity, specify the maximum size that the disk image is allowed to reach. Unless you are working with a qcow2 image, you can also set an amount for Allocation that should be allocated initially. If the two values differ, a sparse image file will be created, which grows on demand.

    For qcow2 images, you can use a Backing Store (also called “backing file”), which constitutes a base image. The newly created qcow2 image will then only record the changes that are made to the base image.

  3. Start the volume creation by clicking Finish.

8.2.2.2.3 Deleting volumes from a storage pool
  

Deleting a volume can only be done from the Storage Manager, by selecting a volume and clicking Delete Volume. Confirm with Yes.

Warning
Warning: Volumes can be deleted even while in use

Volumes can be deleted even if they are currently used in an active or inactive VM Guest. There is no way to recover a deleted volume.

Whether a volume is used by a VM Guest is indicated in the Used By column in the Storage Manager.