HP StorageWorks XP Remote Web Console Software - Manual (Page 23)

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.
Types of Recordsets
In addition to host update recordsets, the MCU passes control information to the RCU in special
non-update recordsets. These special recordsets indicate when pair status changes and when an
MCU power-off sequence is initiated. These special recordsets maintain sequence numbers in
periods of low host activities.
Figure 3 Selecting and Settling TrueCopy for Mainframe Async Recordsets at the RCU
* Since the recordset has not yet arrived at RCU, S2 does not have a time stamp now.
Inflow Control of Recordsets
As described in the previous sections, both the MCU and RCU create sidefiles for storing TrueCopy
for Mainframe Asynchronous recordsets. Since the sidefiles occupy exclusive space in cache, both
the MCU and RCU perform inflow control to prevent an overload of the storage system's cache
TrueCopy for Mainframe Async Recordset Operations 23