Disk Image Directories

Introduction

By default, Cloudmin will create KVM or Xen virtual disk images in the directory or LVM volume group selected on the Host System page for the virtual system's host. All additional virtual disks will be created in the same location. Virtualization types that use a directory on the host's filesystem will always be placed in a sub-directory under the path specified for the host system.

Cloudmin versions 6.0 and later give you more flexibility in placing disk images and virtual filesystems, using the new Disk Image Directories page. This lets the master administrator define additional paths on host systems that can be selected when a virtual system is created, moved or cloned, instead of using the host system default. For example, this could be used to control if a system is created on storage local to the host, or a directory mounted from a common file server, or faster local disks.

Creating A Shared Disk Image Directory

Before adding a directory to Cloudmin, it should first be created on all the host systems that you intend to use it on. If it will only exist locally, it can either be simply created with the mkdir command, or mounted from an additional local disk, RAID device or LVM logical volume.

If you want to use NFS to share a directory between hosts, it must first be exported from a file server. This could be a dedicated device such as one sold by NetApp, or a Linux system with a suitably large and fast local disk or RAID array. In the latter case, you can use Webmin to export a directory as follows :

  1. SSH into the system as root, and create the directory with a command like mkdir /shared
  2. Login to Webmin (or Cloudmin or Virtualmin) on the system, and go Networking -> NFS Exports.
  3. Click the Add a new export button, and enter /shared into the Directory to export field.
  4. In the **Export to..* field, enter the IPs of the host systems that will share this directory.
  5. Click the Create button, then click Apply Changes.

One a directory is shared, it can be mounted on each of your host systems as follows :

  1. Select the host system from the left menu in Cloudmin, and click on Link to Webmin or Open Webmin
  2. In Webmin on the host, go to System -> Disk and Network Filesystems
  3. Select Network Filesystem from the menu, and click the Add mount button.
  4. In the Mounted As field, enter the directory you are sharing, like /shared
  5. In the NFS hostname field, enter the hostname or IP address of the NFS server setup above.
  6. In the NFS directory field, enter the path exported by the NFS server - this will typically be the same as in step 4.
  7. Click the Create button.

Adding A Disk Image Directory

Once the directory exists on all the hosts you want to use it on, it can be added to Cloudmin as follows :

  1. Login as the master administrator, and go to Host Systems -> Disk Image Directories.
  2. Click the Add a new disk image directory link.
  3. In the Directory path on host field, select Directory on host and enter the path (like /shared) into the adjacent text box.
  4. Fill in the Description field with a short description of the directory.
  5. To limit the hosts on which the directory can be used, select them in the For use on host systems field.
  6. By default virtual systems of any type will be able to use the directory, but you can restrict it to a subset of types by selecting them in the For use by virtualization types field.
  7. If you have created any system owner plans, access to the directory can be limit to owners on those plans using the For use by system owners field. Alternately, you can restrict access to only the root (master administrator) user.
  8. Finally, click the Create button. The directory will now be selectable when creating new virtual systems.

Selecting A Directory At Creation Time

Once you have created a disk directory, you can select it when creating a virtual system of a supported type using the Disk image directory field in the Resource limit options section of the creation form. For Xen and KVM systems, all disk image and config files will be created in that directory instead of the host's default directory or volume group. For OpenVZ and LXC systems, the directory that contains the filesystem will be created below the selected path. However, other configuration files will remain in their regular directories.

If creating a system using the Cloudmin command-line API, you can use the --disk-directory flag follow by a path to specify the path. When creating via the remote API, use the disk-directory parameter followed by the path. In all cases, if creating a system while logged in as a system owner you can only select directories that have been made available to the owner's plan.

Changing The Directory For New Disks

If you add an additional disk to a KVM or Xen system after creation, it will by default be created in the directory selected at creation time. However, this can be changed as follows :

  1. Select the virtual system from the left menu.
  2. Open the Resources category and click on Manage Disks.
  3. In the Default disk image directory section, select an alternate path from the New directory menu, and click Save.

The default can also be changed using the modify-system API command, with the --disk-directory flag.

Moving And Cloning Virtual Systems

By default when a virtual system with a non-standard disk directory is moved, Cloudmin will attempt to keep the same directory on the destination system as was used on the source. If the directory is not available on the destination, the move or clone operation will fail.

Both the forms for moving and cloning a system have a field for selecting a new disk image directory to use, similar to the field on the system creation form. Also, the clone-system and move-system API commands accept the --disk-directory flag followed by a directory to use. The --no-disk-directory flag can be used instead to revert to the default directory on the destination host.

Directory Permissions

As mentioned above, the master administrator (root) can limit access to disk directories by system owners based on their plan. For example, a directory that is mounted from faster and more expensive storage (like RAID or SSD) might be reserved for only a subset of users.

You can also control if system owners are allowed to use the default disk directory or logical volume on host systems, by editing the special Host system default path on the Disk Image Directories page. This entry cannot be renamed or deleted, but its permissions can be changed to restrict access to some system owners, or none at all.