HP StorageWorks XP Remote Web Console Software - Manual (Page 29)

Hitachi TrueCopy for z/OS user guide 29
CAUTION: If the type of difference management is set to "Auto", "Track" or "Cylinder" will be set
automatically according to the number of cylinders of a volume that a pair will be created with. If VLL has
been used, the number of cylinders that you set with VLL software is applied. If the volume that you want to
create a pair with has 10,019 or more cylinders, "Cylinder" will be set. If the volume has less than 10,019
cylinders, "Track" will be set.
TrueCopy Asynchronous recordset operations
The TC390A recordsets contain the TC390A M-VOL updates and the associated control information,
including the time-stamp of the M-VOL update, which enables the RCU to maintain update consistency of
the TC390A R-VOLs. TC390A recordset operations include:
• Creating and storing recordsets at the MCU
• Sending recordsets to the RCU
• Storing recordsets at the RCU
• Selecting and settling recordsets at the RCU
• Types of recordsets
• Inflow control for sidefiles
Creating and storing recordsets at the MCU
When an MCU performs an update (host-requested write I/O) on a TC390A M-VOL, the MCU creates a
TC390A recordset that contains: the updated record, time-stamp information, sequence number, record
location (device, cylinder, track, record number), and record length. The TC390A recordsets are queued in
the cache storage of the MCU and sent to the RCU independent of host I/O processes. The RCU uses the
time-stamp and sequence number information in the recordsets to update the R-VOL(s) in the same order as
the M-VOL(s).
The time-stamp information is acquired from the (MVS) host’s I/O time-stamp function. This time stamp
provides a protective measure for write-dependent applications and minimizes recovery time in the event of
a disaster. The sequence number indicates the number of recordsets that the MCU has created for each
consistency group. The recordset information, except for the updated records, is stored and queued in an
area of cache known as sidefile cache. For more information on sidefile cache, see ” Inflow control of
recordsets ” on page 31.
Sending recordsets to the RCU
The MCU sends the TC390A recordsets to the RCU in a similar manner to the TC390 Synchronous
updates. The MCU’s RCPs and/or initiator ports act as host processor channels and issue special I/O
operations, called remote I/Os (RIOs), to the RCU. The RIO transfers the recordsets in FBA format (not
CKD) using a single channel command, eliminating the overhead associated with FBA-CKD conversion
and thus providing more efficient transfer of user data. The MCU can send several recordsets using a single
RIO, even if their sequence numbers are not contiguous. Therefore, TC390A recordsets are usually sent to
the RCU in a different order than the arrivals at the MCU. The RCU ensures that records are applied to the
R-VOLs in the correct sequence. This method of remote I/O provides the most efficient use of MCU-to-RCU
link resources.
NOTE: The parameter length and detailed specification of this TC390A channel command are different
than for TC390 Synchronous RIOs. Verify that your channel extenders are capable of supporting this
command. For further details, contact your HP account support representative.
Storing recordsets at the RCU
The RCU maintains queues to control the storing of recordsets in the sidefile and commitment of updating
records in the R-VOLs. The RCU queuing mechanism uses time-stamping to control the sequence in which
R-VOL updates are applied and uses sequence numbers provided by the MCU to check for any missing
updates.