Mainframe Enablers TimeFinder SnapVX and zDP 8.5 Product Guide

zDP creates snapsets up to the value of the MAX_SNAPSETS parameter. When the maximum number of snapsets is reached, zDP terminates the snapsets based on the termination policy.

A MAX_SNAPSETS value exceeding 256 requires that all source devices in the VDG reside on storage systems running PowerMaxOS 5978.0300 and later. For lower levels of the operating environment, the maximum number of snapsets is 256.

You must redefine the VDG to change the MAX_SNAPSETS parameter from a value less than or equal to 256 to a value exceeding 256. Dynamic change from a MAX_SNAPSETS value less than or equal to 256 to a value exceeding 256 is not allowed.

If the MAX_SNAPSETS value cannot be reached due to other existing snapshots on the devices in the VDG, zDP stops. In this case, query the devices in the VDG and determine whether existing snapshots should be terminated, or the MAX_SNAPSETS value should be lowered. Once the MAX_SNAPSETS value has been reached, zDP is in a steady state and not affected by external snapshot creation.

If the MAX_SNAPSETS value is changed to a value lower than the current number of snapsets in a VDG, zDP continues to only terminate one snapset each time a new snapset is created. Thus zDP effectively maintains the current snapset count even if the count is higher than the MAX_SNAPSETS value. To lower the total snapset count in a VDG, run the TERMINATE VDG command manually.

Calculating the snapset limit with saved and secure snapsets

Use the following formulas when setting the snapset limit for your configuration under PowerMaxOS 5978.0300 and later:

Configuring SECURE on both CYCLE_TIME and SAVED_SNAPSETS

If both SAVED_SNAPSETS and CYCLE_TIME are specified with the SECURE option and the result of 1440*(retention+keepexp)/((skip+1)*interval) is a fraction, the CYCLE_TIME setting takes precedence over SAVED_SNAPSETS to prevent attempts to create a secure snapset within the same cycle. The MAX_SNAPSETS value must be large enough to accommodate the number of secure snapsets created per CYCLE_TIME.

If both SAVED_SNAPSETS and CYCLE_TIME are specified with the SECURE option and the result of 1440*(retention+keepexp)/((skip+1)*interval) is a whole number, the two settings act independently. The MAX_SNAPSETS value must be large enough to accommodate the number of secure snapsets that are created per both CYCLE_TIME and SAVED_SNAPSETS.