Hitachi G200 User Manual page 56

Network settings
3-28
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
Item
• In an environment in which a delay occurs in a line
between storage systems, such as long-distance
connections, you must set an optimal window size of iSCSI
ports in storage systems at the primary and secondary
sites after verifying various sizes. The maximum value you
can set is 1024 KB. The default window size is 64 KB, so
you must change this setting.
• iSCSI ports do not support the fragmentation (splitting
packets) functionality. When the value for the maximum
transfer unit (MTU) of a switch is smaller than the MTU
value of the iSCSI port, packets are lost, and
communication might not be performed correctly. The MTU
value for the switch must be the same as or greater than
the MTU value for the iSCSI port. For the MTU setting and
value, see the switch manual. The MTU value for the iSCSI
port must be greater than 1500.
In a WAN environment in which the MTU value is smaller
than 1500, fragmented data cannot be sent or received. In
this environment, set a smaller value for the maximum
segment size (MSS) of the WAN router according to the
WAN environment, and then connect the iSCSI port.
Alternatively, use iSCSI in an environment in which the
MTU value is 1500 or greater.
• A port can be used for connections to the host (target
attribute) and to a storage system (initiator attribute).
However, to minimize the impact on the system if a failure
occurs either in the host or in a storage system, you should
connect the port for the host and for the storage system to
separate front end modules.
• Disable the spanning tree setting on the port of a switch
connecting to an iSCSI port. If you enable the spanning
tree functionality of a switch, packets might not be looped
in the network when the link is up or down. If this
happens, the packets might be blocked for approximately
30 seconds. If you must enable the spanning tree settings,
enable the port fast functionality of the switch.
• In a network path between storage systems, if you use a
line that has a slower transfer speed than the iSCSI port,
packets are lost, and the line quality is degraded.
Configure the system so that the transfer speed for the
iSCSI ports and the lines is the same.
• Delay in a line between storage systems varies depending
on the system environment. Therefore, validate the system
first, and then check the optimum window size settings of
iSCSI ports. If the impact of the line delay is determined to
be unacceptable, consider using devices for optimizing or
accelerating the WAN speed.
• When iSCSI is used, packets are sent or received using
TCP/IP. Because of this, the amount of packets might
exceed the capacity of a communication line, or packets
might be resent. As a result, performance might be greatly
affected. Use Fibre Channel data paths for critical systems
that require high performance.
Planning for TrueCopy
Considerations