In order to use snap units, the snap pairs must be activated in a snap session on Symmetrix using /ACTIVATE-SNAP. (Snap pairs for ETERNUS DX/AF and VMAX3 are activated immediately after they have been created.) Activation for Symmetrix can take place after the snap session has been created provided the snap pair has the CREATED status.
Activation means two things:
The Copy-On-First-Write process starts: as soon as data is modified on the original unit, the original data is written to the snap unit (to the save pool).
The original unit and snap unit are split, i.e. both can be accessed separately by applications from the server.
The snap pairs which are activated can be selected in different ways: By means of their VSN, their mnemonic name, their internal Symmetrix number, or the ID of the pubset or volume set to which they belong. The most frequent method is selection via the pubset ID, which enables all snap pairs of this pubset to be activated. This method is described below.
Pubset
All snap pairs in a pubset are activated using the command
/ACTIVATE-SNAP UNIT=*BY-PUBSET(PUBSET=<cat-id>,...),...
Further sequence of operations
/UNLOCK-DISK is executed internally for all snap units (see the “Commands” manuals [1]) provided these are attached.
Console message NDE0050 indicates that the activation process has been completed. After the split process has been completed, the status can also be displayed using /SHOW-SNAP-SESSION-STATUS.
When all snap units of a pubset have been activated, the snap pubset can be imported as soon as the split process has been completed and the COPY-ON-WRITE or COPIED status has been assumed. The associated MRSCAT entry is automatically created or updated.
Sufficient space must be available for activation in the save pool, see “Save pools” and “Monitoring the save pools” in "Snap units (Symmetrix)".