HP StorageWorks XP Remote Web Console Software - Manual (Page 25)

Hitachi TrueCopy for z/OS user guide 25
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
XP12000/XP10000 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.
Figure 3 TrueCopy remote copy operations
Initial copy operations
The initial copy operation synchronizes the M-VOL and R-VOL independently of host I/O processes. The
initial copy operation is the same for TC390 Synchronous and TC390A pairs. A TC390 initial copy
operation takes place when you add a new pair or resume a suspended pair. When a new pair is
established, the entire contents of the M-VOL are copied to the R-VOL cylinder by cylinder, including the
VTOC (volume table of contents) but not including the diagnostic and unassigned alternate tracks. For new
pairs, you can also select No Copy or None for the initial copy mode, which copies only the VOLSER
(volume serial number) to the R-VOL. If No Copy or None is selected, the user is responsible for ensuring
that the M-VOL and R-VOL are already identical. The MCU cannot verify the contents of the volumes. When
a suspended pair is resumed (also called a resync operation), only the VOLSER and out-of-sync cylinders
(updated by write I/Os while the pair was suspended) are copied to the R-VOL.
For additional flexibility, TC390 provides the following options for the initial copy operation:
• Use the number of tracks option to specify how many tracks are copied simultaneously by the TC390
initial copy operation when adding/resuming a TC390 pair. This option can be specified using TC390
through XP Command View Advanced Edition Software or XP Remote Web Console (Add Pair-Option)
and the CESTPAIR TSO command (PACE parameter).
• Use the Initial Copy Parameters: Priority option to specify the order in which the initial copy operations
are performed when adding/resuming multiple TC390 pairs. This option can only be specified using
TC390 through XP Command View Advanced Edition Software or XP Remote Web Console (Add Pair).
• Use the Maximum Initial Copy Activities option to specify the maximum number of concurrent initial
copy and resync operations that each MCU can perform (not pair-specific). This option can only be
specified using TC390 software (not PPRC) through XP Command View Advanced Edition Software or
XP Remote Web Console (RCU Option window).
Update copy operations
A TC390 update copy operation occurs when the host issues a write I/O operation to the M-VOL of a
TC390 pair. The update copy operation duplicates the M-VOL write I/O at the R-VOL to keep the M-VOL
and R-VOL synchronized. TC390 provides two modes for update copy operations: synchronous and
asynchronous. The update copy mode is specified when you add a TC390 pair and cannot be changed.
TC390 can also specify whether the cache-fast-write (CFW) data is included in the update copy
operations.
For synchronous update copy mode, the MCU ensures that the M-VOL and R-VOL are synchronized at all
times. The MCU does not return device-end status for the M-VOL write I/O until both the M-VOL write and