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Network Design Guidelines of Configuring EqualLogic iSCSI

This article provides guidelines for designing networks for using EqualLogic iSCSI with a cluster.

Typically you will have a minimum of three networks in use:

• Public networks for applications. A data network can be made redundant using NIC teaming or by using multiple interfaces on separate subnets.

• Private network also called as Heartbeat network. NIC teaming cannot be used
on the Private network.


• Storage area network (SAN). The SAN can be made redundant by use of Microsoft’s
multipath I/O (MPIO). NIC teaming can be used in a SAN; however, multipath I/O provides
more intelligent, SAN-integrated load balancing capabilities.

Each network (public or private) connecting the nodes of a cluster must be configured as a
unique IP subnet. The IP subnet numbers for the networks connecting the cluster nodes must be
different. For example, if a cluster node has multiple adapters attached to the same cluster
network (and NIC teaming is not in use), only one adapter will be used by the Cluster service; the
others will be ignored. A node having two or more network adapters without NIC teaming
connected to the same network will not provide fault tolerance or load balancing and is not

It is recommended that each public network and SAN be configured in a redundant fashion to
provide the benefit of a no-single-point-of-failure configuration. This configuration would
include multiple network switches so that each network can operate (and fail) independently.
The SAN must be a network separate from each public network and private network. On the SAN, each cluster node must have network connectivity to the iSCSI group IP address. You can configure the SAN on the same or separate switches as the public and private networks. If using the same switches, you must use separate VLANs and TCP/IP subnets for each network. On your SAN, you can use either the Microsoft iSCSI Software Initiator or iSCSI HBAs. When using iSCSI HBAs, ensure that you configure these cards to use Storport drivers.

For optimal performance and high availability, EqualLogic recommends following these SAN
network guidelines:

• Use a switched, Gigabit Ethernet network. The connection is 10 and 100 Mbits, the performance will be significantly degraded.

• Utilize fast convergence/fast spanning tree. You will need to consult your switch manufacturer’s documentation to verify if your switches are RSTP-capable and how to configure for RSTP.

• Use flow control. Enable Flow Control on each switch port that handles iSCSI traffic. If
your server is using a software iSCSI initiator and NIC combination to handle iSCSI traffic,
you must also enable Flow Control on the NICs to obtain any performance benefit.

• Enable Jumbo Frames. If supported by all the devices in the network path between hosts and
arrays, enable Jumbo Frames on each switch that handles iSCSI traffic. This support is
usually disabled by default. If your server is using a software iSCSI initiator and NIC
combination, you must also enable Jumbo Frames on the NICs that handle iSCSI traffic to
obtain any performance benefit and ensure consistent behavior.

• Configure multiple network interfaces on an array. Connect them to different switches.

• For a multi-subnet iSCSI group, provide access to the subnet on which the group IP
address for all enabled network interfaces on the group members.

• Use redundant paths between iSCSI initiators and storage arrays. Multipath I/O ensures that
no single point of failure exists between initiators and arrays. This can be achieved by using
Microsoft’s MPIO solution.

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