Network Considerations - IBM Midrange System DS4000 Series Hardware Manual

Generally, three types of options are available, as detailed in Table B-1.
Table B-1 Adapter technologies comparison
Description
Function
Server CPU resource
required
Requires Software
based initiator
Performance

Network considerations

You can run the iSCSI protocol on the DS5000 series of storage subsystems, but you must
consider a number of areas with regard to networked traffic. With normal FC SAN
configurations, little planning is required because of the capacity and robustness of the
switching and connectivity infrastructure or fabric. This is because Fibre Channel provides a
very low-latency and high bandwidth communications medium between the initiator and the
target. It has been specifically designed and implemented for high speed data (disk and tape)
traffic. With iSCSI, these same statements might not be true and can be subject to external
influences outside the traditional SAN itself, such as the existing aforementioned workload of
the TCP/IP network.
Because iSCSI is hosted using a traditional Ethernet network, many of the same
considerations that apply to file-level Networked Attached Storage (NAS) devices also will
apply. You should analyze and understand the impact of the network into which an iSCSI
target is to be deployed prior to the actual installation and configuration of a DS5000 storage
subsystem.
Before beginning an iSCSI deployment, understand and document the network topology that
will be used for the SAN. A poorly understood or inadequate networking infrastructure will
inevitably lead to what is perceived as poor storage performance. Ensure that you connect a
DS5000 storage subsystem with iSCSI host connectivity to the desired initiator using a
dedicated 1 Gbps Ethernet network with as few "hops," or switched and routed connections,
as possible due to propagation loss and latency. Typically, approximately 1 ms of latency is
added for every 100 miles of networked infrastructure, as well as additional latency of up to
1 ms for every routed connection. Thus, connectivity between an iSCSI initiator and an iSCSI
target over a LAN is considered ideal and allows for adequate response time metrics between
a given application and the underlying storage being used.
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IBM Midrange System Storage Hardware Guide
NIC TOE
Network Interface TCP/IP Offload
Card: Provides Engine: A specialized
Ethernet connectivity. NIC that provides
additional functionality.
Physical and data link TCP/IP physical and
communications. data link
communications.
iSCSI protocol iSCSI protocol
management and management.
TCP/IP protocol
management.
Yes. Yes.
Fair. Good.
iSCSI HBA
An HBA that provides
Ethernet connectivity
and additional
functionality.
iSCSI read/write
processing, TCP/IP
processing, and
physical and data link
communication.
None.
No.
Best.