Generation numbers
It is possible to have multiple snapshots with the same name for the same set of source volumes, and generation numbers identify the different snapshots. Generation numbers are relative to existing snapshots at the time of creating or displaying snapshots, and they change as snapshots are created and terminated. For example, if a recent snapshot is terminated, all older snapshots have their generation number decreased by one.
The most recent snapshot always has generation 0. and all previous sessions have their generation numbers incremented by one. Similarly, if a more recent snapshot is terminated, all older snapshots have their generation numbers decreased by one.
Snapset IDs
A snapset refers to a set of consistent snapshots that are taken together. If an SG contains 10 devices and a snapshot is taken, there will be 10 consistent snapshots in the resulting snapset. A snapset is identified by an absolute, unique snapset ID.
Snapset IDs are unique 64-bit integers. This ID is generated by PowerMaxOS. It is guaranteed to be the same for all the snapshots in a Snapset. Snapset ID values represent the time (from the point of view of the array) the snapshots were actually taken. Larger values correspond to snapshots taken after ones with smaller values.
The snapset ID gives you a specific value making managing snapshots, especially restoring easier.
Snapset IDs are supported for manual snapshots and policy snapshots as well for arrays running PowerMaxOS 5978.669.669 or higher.
Solutions Enabler V9.2 with arrays running PowerMaxOS 5978.669.669 supports Snapshot policies to request a stream of consistent snapshots to be automatically taken for applications based on user-defined schedules. The symsnapvx CLI reports both the automated and the manual snapshots on a device. Snapshots can be distinguished by the snapshot type flag.
Solutions Enabler V9.1 or higher with arrays running PowerMaxOS 5978.444.444 or higher supports reporting all the snapshots on a device, including Automated Snapset Creation with Data Protector for z Systems (zDP) snapshots. Snapsets created by zDP are not visible to previous versions of Solutions Enabler. To overcome this, a manual snapshot is created in PowerMaxOS when a pre-9.1 version of Solutions Enabler requests snapshot data for devices against which there are new type of zDP snapsets. This snapset will be in a state that trips the interaction rules of concern ensuring that the older Solutions Enabler will not perform dangerous operations on these devices.
When a device is the target of new zDP snapset the system returns one dummy link target record with the correct source and target devices for the actual link. The link dummy record has the same copy/nocopy state as the actual Automated snapset record. If a device is link –nocopy target then all NDM and SRDF control actions are blocked on that device. Manufactured snapshots are reported with the snapshot name “_Automated_Snapshot”.
