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Manual Chapter: Managing vCMP Virtual Disks
Manual Chapter
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Overview: Managing virtual disks

A virtual disk is the portion of disk space on a slot that the system has allocated to a guest. For example, if a guest spans three slots, the system creates three virtual disks for that guest, one for each guest. Each virtual disk is implemented as an image file with an .img extension, such as guest_A.img.

The vCMP system automatically creates a virtual disk when you create a vCMP guest. However, after you have created and deployed all guests, you can manage the virtual disks on the system as a way to optimize performance. You must be logged into the vCMP host to manage virtual disks on the system.

Using the BIG-IP Configuration utility or the Traffic Management Shell (tmsh), you can delete virtual disks on the system as a way to optimize disk space.

About virtual disk allocation

For each slot that you assign to a guest, the host allocates a fixed amount of disk space (typically 100 gigabytes) for that guest virtual machine (VM). This amount of disk space remains fixed regardless of the number of cores per slot that you configure for that guest. For example, a slot with two cores allocated to guest_A provides the same amount of available disk space for the guest as a slot with four cores allocated to that guest.

Note that you cannot explicitly create virtual disks; instead, the BIG-IP system creates virtual disks when the guest changes to a Provisioned or Deployed state. You can create a guest that remains in the Configured state, but in this case, the guest has no virtual disk allocated to it.

About virtual disk images

A virtual disk is in the form of an image that resides in the /shared/vmdisks directory on each physical blade. The default file name that the BIG-IP system initially assigns to a virtual disk is the guest name plus a .img extension (for example, guestA.img). You identify and manage virtual disks on the system using these file names.

A copy of the virtual disk image for a guest resides on each slot pertaining to that guest (either a single slot or all slots, depending on the guest configuration).

About virtual disk detachment and re-attachment

When a vCMP guest has no virtual disk and moves from the Configured state to the Provisioned state, the system creates a virtual disk and attaches the disk to the guest. This attachment ensures that only that guest can use the virtual disk. A guest can have only one virtual disk attached to it at any one time.

A virtual disk can become unattached from a guest when you perform one of these actions:

  • Delete a guest.
  • Change the Virtual Disk property of the guest to None. Note that to perform this action, you must first change the guest state to Configured.

With either of these actions, the system retains the virtual disks on the system for future use.

You can attach an existing, unattached virtual disk to a new guest that you create. Attaching an existing virtual disk to a newly-created guest saves the BIG-IP system from having to create a new virtual disk for the guest.

Detaching virtual disks from a vCMP guest

Before you can detach a virtual disk from a guest, you must be logged into the vCMP host. Also, you must change the Requested State property on the guest to Configured.
You can detach a virtual disk from the guest, but retain the virtual disk on the BIG-IP system so that you can attach it to another guest later.
Important: Unattached virtual disks consume disk space on the system. To prevent unattached virtual disks from depleting available disk space, routinely monitor the number of unattached virtual disks that exist on the system.
  1. On the Main tab, click vCMP > Guest List. This displays a list of vCMP guests on the system.
  2. In the Name column, locate the relevant guest name, and to the left of the name, select the check box.
  3. Click the Configured button.
  4. In the Name column, click the guest name.
  5. From the Virtual Disk list, select the default value, None.
  6. Click Update.
The vCMP guest no longer has any virtual disk attached to it.

Viewing virtual disks not attached to a vCMP guest

Before you can view unattached virtual disks, you must be logged into the vCMP host.
You can view virtual disks that are not attached to a vCMP guest so that you can monitor virtual disks that might be unused but still consuming disk space.
  1. On the Main tab, click vCMP > Virtual Disk List.
  2. Locate the Virtual Disk List area of the screen.
  3. To the right of the list of virtual disk names, note any disks that do not have any guest names associated with them. These disks are unattached.

Attaching a detached virtual disk to a vCMP guest

Before you begin this task, ensure that:

  • You are logged into the vCMP host.
  • The guest to which you are attaching the virtual disk is in the Configured state.
  • The virtual disk is not currently be attached to another guest.

It is possible for a virtual disk to become detached from a vCMP guest. A disk that is no longer attached to a guest is known as an unattached virtual disk.

You can attach an unattached virtual disk to another guest either when you create the guest or when you modify the Virtual Disk property of a guest.

  1. On the Main tab, click vCMP > Guest List. This displays a list of vCMP guests on the system.
  2. In the Name column, click the name of the vCMP guest that you want to view.
  3. From the Properties list, select Advanced.
  4. From the Virtual Disk list, select a file name. The guest uses the newly-selected virtual disk when being deployed.
  5. Click Update.

About virtual disk migration

In some cases, the virtual disk for a guest migrates automatically from one slot to other slots, or from multiple slots to one slot. You do not need to explicitly manage this migration.

Virtual disk migration occurs when you change the state of a single-slot guest from Provisioned to Configured, and then back to Provisioned. In this case, the system moves the guest to a new slot, copying the virtual disk also.

Deleting a virtual disk from the BIG-IP system

Before deleting a virtual disk, ensure that you are logged into the vCMP host.

Using the BIG-IP Configuration utility, you can delete a virtual disk from the system.

Important: This is the only way to delete a virtual disk from the system. If you delete the associated guest instead, the system retains the virtual disk for re-use by another guest later.
  1. On the Main tab, click vCMP > Virtual Disk List.
  2. Locate the Virtual Disk List area of the screen.
  3. In the Name column, locate the name of the virtual disk that you want to delete.
  4. To the left of the virtual disk name, select the check box.
  5. Click Delete. The system prompts you to confirm the delete action.
  6. Click Delete.
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