# The drive link plug-in

The EVMS drive link plug-in is an aggregating plug-in that combines storage objects into a single object. The resulting drive link storage object can be made into a compatibility volume, EVMS volume, or even be consumed by higher-level storage objects. The drive link plug-in is one way to create large storage objects and volumes from smaller individual pieces.

## How drive linking is implemented

The drive link plug-in consumes storage objects, called link objects, producing a larger drive link object whose address space spans the link objects. The drive link plug-in knows how to assemble the link objects so as to create the exact same address space every time. The information required to do this is kept on each link child as persistent drive-link metadata. During discovery, the drive link plug-in inspects each known storage object for this metadata. The presence of this metadata identifies the storage object as a link object. The information contained in the metadata is sufficient to:

- Identify the link object itself.

- Identify the drive link storage object that the link object belongs to.

- Identify all link objects belonging to the drive link storage. object

- Establish the order in which to combine the child link objects.

If any link objects are missing at the conclusion of the discovery process, the drive link storage object contains gaps where the missing link objects occur. In such cases, the drive link plug-in attempts to fill in the gap with a substitute link object and construct the drive link storage object in read-only mode, which allows for recovery action. The missing object might reside on removable storage that has been removed or perhaps a lower layer plug-in failed to produce the missing object. Whatever the reason, a read-only drive link storage object, together logging errors, help you take the appropriate actions to recover the drive link.

## Creating a drive link

The drive link plug-in provides a list of acceptable objects from which it can create a drive link object. When you create an EVMS storage object and choose the drive link plug-in, a list of acceptable objects is provided that you simply choose from. The ordering of the drive link is implied by the order in which you pick objects from the provided list. After you provide a name for the drive link, the identified link objects are consumed and the new drive link object is produced. There are no create options.

## Expanding partitions

Drive links are aggregating objects that can be expanded in the following ways:

- By adding an additional storage object to the end of the drive link.

- By expanding the last storage object in the drive link.

If the expansion point is the drive link storage object, you can perform the expansion by choosing from a list of objects that the drive link plug-in finds acceptable for the expansion. Multiple objects can be selected and added to the drive link.

If the expansion point is a link object, then the plug-in that produced the link object does the expansion. For example, if the link object was a segment, then the segment manager plug-in that produced the storage object expands the link object. Afterward, the drive link storage object is resized to reflect the expansion.

There are no expand options.

## Shrinking a drive link

Drive links can be shrunk in the following ways:

- By removing link objects from the end of the drive link.

- By shrinking the last storage object in the drive link.

Removing a link object from anywhere other than the end of the drive link produces a gap in the drive link address space, similar to the gap produced by missing link objects. The drive link plug-in attempts to orchestrate the shrinking of a drive-link storage object by only listing the last link object. If you select this object, the drive link plug-in then lists the next-to-last link object, and so forth, moving backward through the link objects to satisfy the shrink command.

There are no shrink options.

## Deleting a drive link

A drive link can be deleted as long as it is not currently a compatibility volume, an EVMS volume, or consumed by another EVMS plug-in.

No options are available for deleting a drive link storage object.