A distinction is made between original unit and snap unit.
The original unit is generally in the READY status. It can be mirrored by RAID, SnapOPC+, EC, REC (ETERNUS DX/AF), TimeFinder (Symmetrix), TimeFinder SnapVX (VMAX3), or SRDF (Symmetrix/VMAX3) .
The snap unit cannot be mirrored. The relevant status of the snap unit is determined by the status of the snap session.
From the SHC-OSD viewpoint the lifetime of a snap session is the lifetime of a snap pair, i.e. it extends from the time it is created (/START-SNAP-SESSION) to the time it is terminated (/STOP-SNAP-SESSION).
During its lifetime, a snap session can assume one of the following statuses:
CREATE-IN-PROG
Relevant for SnapOPC+ and TimeFinder/Snap.
The snap session (the snap pair) is currently being created (Symmetrix) or is currently being created and activated (ETERNUS DX/AF), i.e. the snap unit is currently being connected to the original unit.
The snap unit is in the NOT-READY status.
CREATED
Relevant for TimeFinder/Snap.
The snap session has been created, i.e the snap unit is connected to the original unit but has not yet been activated.
The snap unit is in the NOT-READY status.
COPY-ON-WRITE
Relevant for SnapOPC+, TimeFinder/Snap, and TimeFinder SnapVX.
The snap session is activated. The original unit and snap unit can be processed separately. Only the original versions of modified data are copied onto the volumes provided for this purpose.
In addition for TimeFinder SnapVX: the snap unit has a link to the snapshot. This status is also reached after the (possibly multiple) /RESTORE-FROM-SNAP command(s).
Changes on the snap unit are only local. The snapshot remains unchanged.
The snap unit is in the READY status.
COPIED
Relevant for TimeFinder/Snap.
The snap session has been activated; 100% of the snap unit data is contained on the save devices, i.e. no track pointer now points to the original.
The snap unit is in the READY status.
The COPIED status does not correspond to the normal application for snap units because the latter are envisaged for original units with only a low level of updating.
REST-IN-PROG The original unit is reconstructed from the snap unit; the saved data is copied from the snap unit to the original unit.
The snap unit is in the NOT-READY status (Symmetrix).
The snap unit is in the READY status (ETERNUS DX/AF and VMAX3).
RESTORED
Relevant for TimeFinder/Snap and TimeFinder SnapVX.
The original unit has been fully reconstructed from the snap unit.
The snap unit is in the NOT-READY status.
SNAP-RESTORED
Relevant for TimeFinder SnapVX.
The original unit has been fully reconstructed from a snapshot (not from the snap unit). Multiple reconstruction is possible. It is independent of whether the snapshot is connected with a snap unit.
The snap unit is in the NOT-READY status.
UNUSED
Relevant for SnapOPC+ and TimeFinder/Snap and TimeFinder SnapVX.
The snap unit is not connected to any original unit. It is free for a /START-SNAP-SESSION. The special VSN S#<mn> is output for VMAX3 (no preconfigured snap devices), see section "Automatic selection of snap units"
The snap unit is in the NOT-READY status.
TERM-IN-PROG
Relevant for TimeFinder/Snap and TimeFinder SnapVX.
The snap session is in the process of being terminated.
The snap unit is in the NOT-READY status.
FAILED
Relevant for SnapOPC+ and TimeFinder/Snap and TimeFinder SnapVX.
The snap session has become unusable (e.g. because of a save pool overflow); the data on the snap unit is lost. The session can only be terminated using /STOP-SNAP-SESSION.
The snap unit is in the NOT-READY status.