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.
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.
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).
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:
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.
Before you begin this task, ensure that:
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.
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.
Using the BIG-IP Configuration utility, you can delete a virtual disk from the system.