QoS

Configure the differentiated services code point (DSCP) value of 3 to be applied to all outgoing IP packets in this iSCSI interface. The valid range for the iSCSI DSCP value is from 0 to 63.

Reverts the switch to its factory default (marks all packets with DSCP value 0).

iSCSI Routing Modes

Each mode negotiates different

operational parameters, has different advantages and disadvantages, and is suitable for different usages.

Pass-thru mode

In pass-thru mode, the port on the IPS module or MPS 14/2 module converts and forwards read data frames from the Fibre Channel target to the iSCSI host frame-by-frame without buffering. This means that one data-in frame received is immediately sent out as one iSCSI data-in PDU.

In the opposite direction, the port on the IPS module or MPS 14/2 module limits the maximum size of iSCSI write data-out PDU that the iSCSI host can send to the maximum data size that the Fibre Channel target specifies that it can receive. The result is one iSCSI data-out PDU received sent out as one Fibre Channel data frame to the Fibre Channel target.

The absence of buffering in both directions leads to an advantage of lower forwarding latency. However, a small maximum data segment length usually results in lower data transfer performance from the host due to a higher processing overhead by the host system. Another benefit of this mode is iSCSI data digest can be enabled. This helps protect the integrity of iscsi data carried in the PDU over what TCP checksum offers.

Store-and-forward mode (default)

In store-and-forward mode, the port on the IPS module or MPS 14/2 module assembles all the Fibre Channel data frames of an exchange to build one large iSCSI data-in PDU before forwarding it to the iSCSI client.

In the opposite direction, the port on the IPS module or MPS 14/2 module does not impose a small data segment size on the host so the iSCSI host can send an iSCSI data-out PDU of any size (up to 256 KB). The port then waits until the whole iSCSI data-out PDU is received before it converts, or splits, the PDU, and forwards Fibre Channel frames to the Fibre Channel target.

The advantage of this mode is higher data transfer performance from the host. The disadvantages are higher transfer latency and that the iSCSI data digest (CRC) cannot be used.

The store-and-forward mode is the default forwarding mode.

Cut-through mode

Cut-through mode improves the read operation performance over store-and-forward mode. The port on the IPS module or MPS 14/2 module achieves this by forwarding each Fibre Channel data-in frame to the iSCSI host as it is received without waiting for the whole exchange complete. There is no difference for write data-out operations from store-and-forward mode.

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Cisco Systems MDS 9000 setup guide QoS, ISCSI Routing Modes
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MDS 9000 specifications

Cisco Systems MDS 9000 series is a line of storage networking switches designed to address the unique demands of enterprise-level data centers. These switches provide high-performance solutions for connecting various storage devices, including traditional disk arrays, solid-state drives, and tape libraries. The MDS 9000 series is built for scalability, high availability, and advanced security, making it an ideal choice for organizations looking to optimize their storage infrastructure.

One of the standout features of the MDS 9000 series is its support for Fibre Channel and FICON protocols, which enable seamless integration with various storage technologies. This versatility is crucial for organizations that may be using a mix of applications and storage performance requirements. The switches support multiple speeds, including 1G, 2G, 4G, 8G, and even 16G Fibre Channel rates, ensuring that they can adapt to evolving storage needs.

The MDS 9000 is known for its advanced features in terms of management and automation. Cisco provides intelligent automation capabilities to enhance operational efficiency. Features like Flow Vision and intelligent network services allow for deep visibility into storage environments, enabling administrators to monitor performance, troubleshoot issues, and optimize resource allocation effectively. This level of visibility helps organizations to mitigate risks and ensure data availability.

Security is another paramount consideration for the MDS 9000 series. The switches are equipped with a range of security features, including role-based access controls, encryption technologies, and zoning options. These capabilities help safeguard sensitive data and ensure compliance with industry regulations, making the MDS 9000 a trusted choice for enterprises dealing with critical data.

The architecture of the MDS 9000 series is designed for high availability and resiliency. With redundant power supplies and cooling systems, these switches minimize downtime and ensure continuous operation. Additionally, they offer advanced features like non-disruptive software upgrades, which eliminate the need for scheduled outages during firmware updates.

In summary, the Cisco Systems MDS 9000 series offers a robust set of features tailored for enterprise storage networking. Its support for various protocols, intelligent management capabilities, and high availability characteristics make it a preferred choice for organizations seeking to optimize their storage infrastructure for both current and future needs. By investing in the MDS 9000 series, businesses can enhance their operational efficiency, ensure data security, and maintain a competitive edge in today's data-driven landscape.
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