HP StorageWorks XP Remote Web Console Software - Manual (Page 26)

26 TrueCopy for the XP128/XP1024/XP10000/XP12000
NOTE: For information on TC390A configuration services, contact your HP account support
representative.
Asynchronous Consistency Groups
A TC390A consistency group is a user-defined set of volume pairs across which update sequence
consistency is maintained and ensured at the remote site. Each TC390A volume pair must be assigned to a
consistency group. You can use TC390A to configure up to 128 consistency groups (0-7F) for each MCU
and provides group-based operations for consistency groups (for example, suspend and resume group).
You can use consistency groups to maintain update sequence consistency for databases that span multiple
volumes, allowing immediate database recovery at the remote site when needed. For more information on
TC390A consistency group operations, see ” TrueCopy Asynchronous Consistency Group Operations ” on
page 35.
Host I/O Time-Stamping Function
If you plan to establish TC390A consistency groups, the I/O time-stamping function must be installed on
the host processor at the main (primary) site. The I/O time-stamp, which is provided by MVS DFSMSdfp, is
the same time-stamp that is used by IBM XRC pairs. The RCU requires the I/O time-stamp information to
process TC390A recordsets. The I/O time-stamping function should also be installed on the host processor
at the remote (secondary) site so that time-stamps can be used when copying data in the reverse direction.
NOTE: If the main and/or remote system consists of several CPU complexes, a SYSPLEX timer is required
to provide a common time reference for the I/O time-stamping function.
Error Reporting Communications
Error reporting communications (ERC), which transfers information between host processors at the main
and remote sites, is a critical component of any disaster recovery effort. You can configure ERC using
channel-to-channel communications, NetView® technology, or other interconnect technologies, depending
on your installation requirements and standards. Neither TC390 nor Command View XP or XP Remote
Web Console provides ERC between the main and remote sites.
When TC390 is used as a data migration tool, ERC is recommended but is not required. When TC390 is
used as a disaster recovery tool, ERC is required to ensure effective disaster recovery operations. When a
TC390 pair is suspended due to an error condition, the MCU generates sense information, which results in
an IEA491E system console message. This information should be transferred to the remote site through ERC
for effective disaster detection and recovery.
Remote Copy Operations
The following figure illustrates the two types of TC390 remote copy operations: initial copy and update
copy. To reduce the overhead associated with these remote copy activities and maximize data transfer, the
XP128/XP1024/XP10000/XP12000 uses a special write command that is allowed only for TC390 initial
and update copy operations. This command transfers the control parameters and the FBA-format data for
consecutive updated records in a track using a single write operation. The special TC390 write command
reduces interlocks on the ESCON interface protocol as well as the overhead required for performing
FBA-to-CKD and CKD-to-FBA conversions.
Figure 3 TrueCopy remote copy operations