Using CA AppLogic › Appliance Developer Guide › Appliance Overview › Configure Appliance › Set Class Boundary › Volumes

Volumes

Volumes define the set of disk volumes available to the appliance. The types of volumes are as follows:

Instantiable Volumes

Instantiable volumes belong to the appliance class and are copied and migrated with every instance of the catalog class. This is most frequently used for boot volumes containing the OS and writable configuration space, such as \etc or /var/log/temp in Linux appliances. You should not use instantiable volumes or boot volumes to keep persistent state or meaningful user data. Those should be kept on placeholder volumes. For additional information, refer to the Tie Boundary to Interior section.

Important The instantiable volume can be lost between startup of the appliance and will not be preserved on copy and migrate of the application where the appliance resides. An exception to that is a singleton. In a singleton, the instantiable volume is always preserved.

Common Volumes

Common volumes hold read only code and data that applies to the appliance class. These volumes are frequently used to keep large appliance code separated from the boot volume. This ensures that copies of the common volume do not need to be made for the instances of that class.

To provide another layer of configuration assurance, the content of the volume cannot be modified at runtime. For example, you can place Linux appliances in the catalog /usr subdirectory in a common volume to share as read only volume to all instances of this appliance.

In addition, you can reduce the size of the instantiable volume by moving files to the common volumes. You can also use the common volume as a boot volume for appliances that use a read only boot volume, such as the Linux Filer appliance. Most appliances support using a read only boot volume to reduce space; however, it is slightly more complex to use and may preserve log files across re-boots.

Placeholder Volumes

Placeholder volumes are intended for persistent state, appliance-specific content, such as files and databases, as well as fixed content, such as html files for a web server. In addition, you can attach volumes to placeholder volumes. You can use these volumes for content that belongs to the application, rather than the appliance class. Even when the placeholder volume belongs to the application, it is not deleted or replaced when the appliance is copied or updated.

When using an appliance instance, you must configure application volumes into the placeholder volume for the appliance to operate. You should place as few constraints as possible on placeholder volumes and not require any specialized preparation. For example, mysql auto creates a placeholder volume on its database, if it does not exist.

You can use string properties to design the file directory volume on the appliance. For example, web6 has the script_dir and html_dir that are relative to the placeholder volume. Outside of the example, such paths should be relative to the root of the placeholder volume, not the root of the appliance or expose the internal structure of the appliance.

Follow these steps:

1. On the Volumes tab, define the volumes by selecting the row and entering information, as needed.
   • Name - represents the role of the volume for the appliance class. The name is a single, case sensitive word consisting of alphanumeric characters. Device names must be specified for all volumes, or the device names must be left empty for all volumes. If the device names used by the volumes of this class are not updated as specified, the application will fail to start.
   • Mount On - indicates the path, such as /mnt/data, where the volume should be automatically mounted inside of the appliance. If empty, the appliance decides where to mount the volume.

     For Windows appliances, you can only mount boot volumes as c or c:\. The mount path for non-boot volumes can be only one of the following: letter, letter:\, or c:\path where letter is any valid drive letter except for c and path is not empty. If the Configuration Mode is set to DHCP, the mount path is defined automatically.

   • Device - specifies the name of a device with its volume is available to the appliance. For Linux appliances, this is typically in the form of /dev/hdaN, where N is a digit between 1 and 9. If not specified, the appliance uses its etc/fstab configuration file to determine how and where in the filesystem hierarchy the volume is mounted.
   • Boot - indicates the boot volume for the appliance. Each appliance must have a boot volume for the appliance to start.
   • Constraints - specifies the performance constraints, such as none, high bandwidth, and local only. This parameter is ignored and should not be used.
2. Set the following optional parameters, as needed.
   • Read Only - indicates a read only volume
   • Mandatory - indicates a placeholder volume must be attached to the appliance. The appliance refuses to start volumes that are marked as mandatory without a value being specified.
   • Shared - indicates the volume can be shared among multiple appliances. To enable sharing, the volume should also be marked as read only. This value is required for common volume and be set for the placeholder volume.
   • Info - displays the name, size, and filesize.
3. To add or delete a volume, select the volume, then click Add or Delete.

   Delete permanently removes the volume from the class and grid. All volume content is lost and there is no reset. You cannot remove a volume that is currently in use.

4. To rename or resize a volume, click the corresponding button. The Rename or Resize Volume dialog displays.
5. To manage the volumes in a tree directory, click Manage. The information displays in a directory tree.
6. To continue, select the Properties tab.