Белая книга для Cisco Cisco MDS 9000 SAN-OS Software Release 1.0

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White Paper

Connecting Cisco MDS 9000 Family in Heterogeneous Fabrics

Ease-of-migration and investment protection are critical requirements for a storage administrator planning to evolve

multiple isolated SAN islands into an enterprisewide fabric. Specifically, a storage administrator should be able to

build a heterogeneous fabric with SAN switches from multiple vendors. On the surface it sounds like a trivial task.

There should be no problem if vendors adhere to the ANSI T11 FC-SW-2 specification for Fibre Channel switch

interoperability.

Unfortunately, not all switch vendors strictly adhere to this standard, resulting in switch interoperability issues that prevent customers

from building heterogeneous fabrics. Switch vendors support a special mode to address this issue, allowing them to interoperate with

other switches. However, the process of enabling the interoperability mode on existing switches results in fabricwide disruption and

loss of existing functionality. For customers deploying SANs in mission-critical environments, this may not an acceptable solution.

Starting with Cisco

MDS 9000 SAN-OS Software Release 1.2(1) and later, Cisco MDS 9000 Family multilayer directors and fabric

switches interoperate with an installed base of specific switches without disrupting the existing fabric services or losing functionality.

This functionality allows storage administrators to consolidate SAN islands while preserving their investments in existing switches.

CHALLENGE

Standard Interoperability Modes

Both Brocade and McDATA switches support “interop” and “open” modes respectively, which when enabled, allow them to interoperate

with each other and Cisco MDS 9000 switches. These special modes are in addition to the regular modes (enabled by default) in which the

proprietary features are supported. These special modes result in the following when enabled:

●

Fabric disruption—The interoperability mode has to be enabled on each Brocade and McDATA switch in the fabric.

When enabled, this mode causes a switch to either reset (Brocade) or restart (McDATA). For customers deploying SANs

in mission-critical environments this is not an acceptable solution.

●

Loss of functionality—Some of the features that are available prior to enabling the interoperability mode are subsequently

disabled. For example, when “interop” mode is enabled on Brocade switches, it disables domain/port-based zoning, Virtual

Channel flow control, and trunking, etc. This creates operational challenges for storage administrators who have to give up

functionality in order to build heterogeneous fabrics.

Cisco MDS 9000 SAN-OS Software Release 1.0(1) and later support an interoperability mode (mode 1) that allows Cisco MDS 9000

switches to interoperate with Brocade and McDATA switches configured in “interop” and “open” modes respectively. Unlike Brocade

and McDATA modes, the Cisco MDS 9000 interoperability mode (mode 1) can be enabled on a per-virtual SAN (VSAN) basis without

resetting or restarting the Cisco MDS 9000 switches, and it does not impact the features and functionality of other VSANs.