System Performance Considerations; Determining Round Trip Time - Hitachi G200 User Manual

Option
mode
784

System performance considerations

Synchronous copy operations affect I/O performance on the host and on the
primary and secondary systems. TrueCopy provides options for minimizing
the impact and for maximizing the efficiency and speed of copy operations for
the best level of backup data integrity. These options are discussed in:
• Determining Round Trip Time on page 3-5
• Determining Minimum Number of Remote Paths on page 3-7
• Allowing I/O to the P-VOL after a split—Fence Level options on page
3-10
Performance is also optimized with the proper bandwidth. This is discussed in
Analyzing workload, planning data paths on page

Determining Round Trip Time

You specify a time limit in milliseconds for data to travel from the P-VOL to
the S-VOL when you set up the TrueCopy association between primary and
secondary systems. Round Trip Time is used by the systems to control the
initial copy pace when update copying is in progress.
This section provides instructions for determining your system's Round Trip
Time.
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 and
500ms remote IO response time.
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
Allows you to reduce RIO MIH time to 5-seconds. As a result, after a
remote path error, less time elapses until the operation is retried on an
alternate path. (Both RIO MIH time and the Abort Sequence timeout value
are combined for this retry time.)
• ON: Reduces the RIO MIH time to 5-seconds.
Combined with the Abort Sequence timeout value, the total amount of
time that elapses before the operation is retried on another path is a
maximum of 10-seconds.
• OFF: The RIO MIH time that you specified at RCU registration
(default=15 seconds) is used with the specified Abort Sequence
timeout value.
SOM 784 is supported only when the port type of all remote paths in a
single remote connection is Fibre. If the port type of all remote paths in a
single remote connection is iSCSI or if iSCSI and Fibre are mixed, this SOM
is not supported.
Planning for TrueCopy
Description
3-8.
3-5