Source: Symantec Docs

Detach State

Detaching a plex leaves the plex associated with its

volume, but prevents normal volume I/O from being directed

to the plex. This operation can be applied to plexes that

are enabled or disabled. The rules for performing the

detach depend upon the usage types of the volumes involved.

The operation does not apply to dissociated plexes.

Disassociate State

Dissociate each of the named plexes. Dissociating a plex

breaks the link between the plex and its volume. A

dissociated plex is inaccessible until it is reassociated,

which can be done either with vxplex att or with vxmake.

Any checks and synchronizations that apply to the det

operation also apply to the dis operation.

Plex dissociation is the normal means of unmirroring a

volume, or reducing the mirror count for a volume. To

support this use, -o rm can be used to dissociate and

remove the plex (and its associated subdisks) in the same

operation. This makes the space used by those subdisks

usable for new allocations (such as with vxassist or with

vxmake).

Plex dissociation can also be used for file system backups

of volumes that are normally mirrored. Plex devices are not

directly mountable, so the backup method described for the

det operation will not work if the backup program requires

a mounted file system. To support such backup programs, a

plex can be dissociated and can then be allocated to a new

volume, such as with the command:

vxmake -U gen vol volume plex=plex

The created volume can then be started and mounted for use

by the backup program.