Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

About TrueCopy for z/OS Operations 2-21
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Selecting and Settling Recordsets at the RCU
The RCU selects the recordset to be promoted to formal data (or “settled”) as
follows:
1. The RCU checks for a valid entry at the top of each queue in the consistency
group. If the top of any queue is empty (i.e., recordset not yet received), the
RCU waits for that entry.
2. When the top of each queue contains a valid entry (recordset), the RCU
selects the entry which has the earliest time-stamp value, and then settles
this recordset.
3. The RCU repeats steps (1) and (2) to select and settle TCzA recordsets.
Figure 2-3 (next page) illustrates recordset selection and settling at the RCU.
In this example, the top of the queue contains a valid entry: S1/T1. The RCU
selects recordset S1/T1 to be settled, because T1 is the earliest time-stamp.
When S1/T1 is removed from the MCU queue, recordset S2 becomes the top
entry, but it is empty. When recordset S2 arrives (and its time-stamp is later
than T1 and earlier than T3), the RCU selects S2/T2 as the next recordset to
be settled. The recordset selected by the RCU is marked as “host-dirty” and
treated as formal data. The time-stamp value of that recordset is promoted to
the consistency time (C/T) of the group. The RCU settles the updated records
in the recordset as follows:
• If the corresponding track is in cache (track-hit), the updated records in the
recordset are copied to the existing cached track, and the cache space for the
sidefile is released.
• If the corresponding track is not in cache (track-miss), the RCU changes the
cache designation of the sidefile to formal data. The data is not physically
moved.