HP StorageWorks XP Remote Web Console Software - Manual (Page 19)

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Read and Write I/O Operations for TrueCopy Volumes
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S-VOL Write Option
Initial Copy Operation
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 TrueCopy for Mainframe Synchronous and Asynchronous
pairs. A TrueCopy for Mainframe initial copy operation takes place when you add a new pair or
resynchronize a suspended pair. When a new pair is established, the entire contents of the M-VOL
are copied to the R-VOL by track, including the VTOC (volume table of contents) but not including
the diagnostic and unassigned alternate tracks. If 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 resynchronized, only the VOLSER and out-of-sync tracks
(updated by write I/Os while the pair was suspended) are copied to the R-VOL.
For additional flexibility, TrueCopy for Mainframe provides the following options for the initial
copy operation:
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The Number of Tracks option allows you to specify how many tracks are copied simultaneously
by the TrueCopy for Mainframe initial copy operation when adding/resynchronizing a
TrueCopy for Mainframe pair. This option can be specified using the TrueCopy for Mainframe
software and the CESTPAIR TSO command (PACE parameter).
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The Initial Copy Priority option allows you to specify the order in which the initial copy
operations are performed when adding/resynchronizing multiple TrueCopy for Mainframe
pairs. This option can only be specified using the TrueCopy for Mainframe software (not PPRC).
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The Maximum Initial Copy Activities option allows you 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 the TrueCopy for Mainframe software (not PPRC).
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The Round Trip Time option is a reference value used for automatic control of the initial copy
pace to avoid the remote I/O's response time of the update I/Os being affected by initial
copy. The value of Round Trip Time is compared with the remote I/O response time, and
then, the copy pace is controlled when the difference between the two values is large.
If the difference between the remote I/O response time and the value of Round Trip Time is
large, for example, the remote I/O response time is 500 ms but the value of Round Trip Time
is 1 ms, the copy pace will slow or sometimes the initial copy will interrupt, so that the initial
copy process does not occupy the entire bandwidth of the lines.
On the other hand, if the difference between the remote I/O response time and the value of
Round Trip Time is small, for example, the remote I/O response time is 5 ms and the value of
Round Trip Time is 1 ms, the initial copy continues to run at a specified pace.
The default value of Round Trip Time is 1 ms. Specify an appropriate value at the Round Trip
Time when the distance between MCU and RCU is long or there is a delay caused by the line
equipment. If the initial copy operation is performed with the default value of Round Trip Time
instead of the appropriate value, it may take an unexpectedly long time to complete the initial
copy operation.
Update Copy Operation
A TrueCopy for Mainframe update copy operation occurs when the host issues a write I/O operation
to the M-VOL of a TrueCopy for Mainframe 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. TrueCopy for Mainframe
provides two modes for update copy operations: synchronous and asynchronous. The update copy
mode is specified when you add a TrueCopy for Mainframe pair and cannot be changed. TrueCopy
for Mainframe also allows you to specify whether the cache-fast-write (CFW) data is included in
the update copy operations.
Remote Copy Operations 19