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

2-22 About TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
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,
and also maintain sequence numbers in periods of low host activities.
Grp=n
S1/T1S3/T3S4/T4
Selecting
Recordset
Receiving
Recordsets
S1/T1
Settling
Recordset
Consistency
Time
Formal
Data
T1
Data
Grp=n
S2*
Si = sequence number which shows the order that
write I/Os are received from MCU
(S2 = S1+1, S3 = S2+1, S4 = S3+1).
Ti = time stamp which shows the time of receiving write I/O
from MCU (T1 < T2 < T3 < T4).
* Since the recordset has not yet arrived at RCU, S2 does not have a time stamp now.
Figure 2-3 Selecting and Settling TrueCopy for z/OS Async Recordsets
at the RCU