HP XP Racks - Manual (Page 17)

Note the following Round Trip Time considerations:
•
If the difference between Round Trip Time and remote IO response time is significant, the
system slows or even interrupts the initial copy operation so that the update copy can continue.
Example of significant difference between the two: 1ms RT Time : 500ms remote IO response
time.
•
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 : 5 ms
To determine Round Trip Time value
The value of Round Trip time= round trip time between MCU-RCU x 2(*) + initial copy response time (ms)
(*) A data transfer between primary and secondary system 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 your service provider, or use a ping
command. If you do not use channel extenders between the primary and secondary system,
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 copy VOLs, and the bandwidth of the
channel extender communication lines between primary and secondary system.
Initial copy response time (ms) = (1[MB] / "Data path speed between MCU-RCU[MB/ms]
1
") x ("initial copy
pace(
2
/ 15) x (number of maximum initial copy VOLs
3
" / "Number of data paths between MCU-RCU"
4
)
1. When you connect MCU with RCU without channel extenders, specify 0.17[MB/ms] in "Speed of line between
MCU and RCU".
2. For "initial copy pace" in the preceding formula, see the following table.
3. For "number of maximum initial copy volumes", use the value set up per storage system. The default is 64.
4. Even if the "number of maximum copy VOLs" / "Number of data paths between MCU-RCU" is larger than
16, specify "number of maximum initial copy VOLs" / "Number of data paths between MCU-RCU" as 16.
The following table shows the initial copy pace used for the response time calculation.
Initial, update copy in progress Initial copy only in progress Interface
When initial copy pace specified
at the time of pair creation is 9 to
15 When initial copy pace specified
at the time of pair creation is 1 to
8
8 User-specified value between 1
and 8 User-specified value RAID Manager
8 User-specified value between 1
and 8 User-specified value Remote Web
Console
System performance considerations 17