Hitachi G200 User Manual page 34

• If the difference between the two is insignificant, initial copying is allowed
to run at the specified pace.
Example of insignificant difference between the two: 1ms RT Time and 5
ms remote IO response time.
To determine Round Trip Time value
The value of Round Trip time= round trip time between primary system and secondary
system x 2(*) + initial copy response time (ms)
(*) A data transfer between primary and secondary systems involves two response
sequences in one command issuance. Therefore, you need to double the round trip time.
• For the "round trip time" in the formula, please ask Hitachi Data Systems
customer support, or use a ping command. If you do not use channel
extenders between the primary and secondary systems, specify "1".)
• The "initial copy response time" in the formula is the response time
required for multiple initial copy operations. With the following formula,
determine the initial copy response time using the initial copy pace, the
number of maximum initial copies, and the bandwidth of the channel
extender communication lines between primary and secondary systems.
Initial copy response time (ms) = (1[MB] / "Data path speed between primary
system and secondary system [MB/ms]
maximum initial copy
secondary system"
1
.
2
.
3
.
4
.
The following table shows the initial copy pace used for the response time
calculation.
3-6
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
3
" / "Number of data paths between primary system and
4
)
When you connect the primary system with the secondary system without
extenders, set "Data path speed between primary system and secondary
system" to either of below depending on the fiber cable link speed.
2 Gbps: 0.17 MB/ms
4 Gbps: 0.34 MB/ms
8 Gbps: 0.68 MB/ms
16 Gbps: 1.36 MB/ms
For "copy pace" in the initial copy response time formula, see the following
table.
For "number of maximum initial copy", use the value set up per storage system.
The default is 64.
Even if the "number of maximum initial copy" / "Number of data paths between
the primary system and secondary system" is 16 or larger, specify "number of
maximum initial copy VOLs" / "Number of data paths between primary system
and secondary system" as 16.
Planning for TrueCopy
1 2
") x ("copy pace" / 4) x (number of