HP XP Racks - Manual (Page 18)

The following table shows example settings.
Round trip
time
specified
[ms] Number of maximum
initial copy VOLs Initial copy pace Number of data
paths between
MCU/RCU Data path speed
between
MCU/RCU
(MB/ms) Round trip time
between MCU RCU
[ms]
160 64 15 4 0.1 0
220 64 15 4 0.1 30
360 64 15 4 0.1 100
Determining Minimum Number of Remote Paths
You specify the minimum number of remote paths to the secondary system when you set up the
Cnt Ac-S association between primary and secondary systems. Using the Minimum Number of
Paths option, you set a minimum value from one to eight paths, with one being the default.
If the number paths in Normal status drops below the specified minimum, the primary storage
system splits the pair to avoid impact to host performance.
•
To maintain high performance in the primary storage system, HP recommends setting the
minimum number at two.
•
For a pair with important data, set the minimum at one. This allows the system to continue
update operations to the secondary system.
•
You can protect data integrity between P-VOL and S-VOL in the event that the system splits the
pair because the number of paths is lower then the minimum. With the Fence Level setting
(specified during the initial copy), you decide whether, when the pair is split due to an error,
the host continues to access the P-VOL or is denied access. See
“Allowing I/O to the P-VOL
after a split—Fence Level options” (page 20) for more information.
Analyzing workload, planning data paths
You optimize copy operations and performance by carefully planning bandwidth, number of data
paths and host interface paths, and number of ports. This is discussed in:
Check with your HP service provider for more information.
•
Analyze write-workload. Bottlenecks severely impact performance, but the workload data you
collect (MB/s and IOPS) help determine the following key elements that, when sized properly,
form a data path that operates free of bottlenecks under all workload levels:
◦ Amount of bandwidth.
◦ Number of data paths.
◦ Number of host-interface paths.
◦ Number of ports dedicated for Continuous Access Synchronous on the primary and
secondary system.
•
If you are setting up Continuous Access Synchronous for disaster recovery, make sure that
secondary systems are attached to a host server. This enables both the reporting of sense
information and the transfer of host failover information. If the remote site is unattended by a
host, you should attach the storage systems to a host server at the main site so that the system
administrator can monitor conditions.
18 Planning for Continuous Access Synchronous