HP 3PAR Remote Copy Software - Manual (Page 122)

5.2 Performance Notes for RCIP Configuration
Remote Copy User’s Guide InForm OS Version 2.3.1
After sending the I/O over a local GigE link, (which is more efficient than sending over a link in
another node), the host writes coming into the nodes with the GigE links are preferentially
sent over the local link. If a node does not have a GigE link, then host writes to that node are
sent equally on the two nonlocal links. Because of this, depending on how the host writes to
the nodes are distributed, the two GigE links might not always have the same traffic rate.
5.1.2 Initial Synchronization
In general, when running Remote Copy on a pair of InServ Storage Servers, the highest link
throughput (MB/s) is achieved during the initial synchronization of the primary and secondary
volumes. During initial synchronization, throughput might be as high as 70 MB per second on a
single GigE link or 125 MB per second on both links when there are multiple volumes
synchronizing.
5.1.3 Distance
As the physical distance between the storage servers in the Remote Copy pair increases, there
might be an increase in latency and a decrease in throughput.
Low bandwidth with high latency and low bandwidth with low latency can be optimized by
using the setrcopytarget tunelinks command. See Appendix B, Remote Copy
Commands for information about the setrcopytarget tunelinks command.
5.1.4 MTU Size
The throughput (MB/s) over GigE networks is affected by the Maximum Transmission Unit
(MTU) size. Remote Copy supports the use of 9000 byte jumbo Ethernet frames, which result in
significantly better throughput and lessens CPU usage on the primary server when compared
to using the default 1500 byte MTU. Depending on workload, you might see as much as a 50
percent increase by using a 9000 byte MTU setting as opposed to a 1500 byte MTU setting.
NOTE: This limitation does not apply to 1-to-N Remote Copy. For 1-to-N Remote
Copy, the primary storage server can have four RCIP interfaces; two to one
secondary system and two to the other secondary system.
NOTE: For instructions on performing the initial synchronization using tape
backup instead of the Remote Copy links, see Initial Synchronization Using Tape
Backup on page 3.38.