Sunday, June 20, 2010


The host-sflow agent is a free, open source, implementation of Host sFlow. Host sFlow extends the visibility provided by the sFlow standard, currently supported by most switch vendors, to include server performance metrics. Adopting a single multi-vendor standard for network and system monitoring simplifies data center management, providing "single pane of glass" visibility in converged data center environments (see Management silos).
    Extending sFlow monitoring to hosts poses some configuration management challenges that are not easily addressed using the current approaches to sFlow configuration in switches:
    1. Scalability, a data center with 100 switches may contain thousands of servers. With virtualization, there may be many virtual machines running on each physical server, pushing the total server count even higher. Automation is essential in order to deploy timely configuration changes and to ensure configuration consistency across all the servers.
    2. Diversity, each host-sflow agent may be running on different operating systems (e.g. Windows, Linux) or a hypervisor (e.g. XenServer, ESXi). While you can generally rely on a switch to support SNMP and provide remote CLI access (using telnet or ssh), these services cannot be relied upon for multi-vendor, multi-OS server configuration.
    In order to address these challenges, host-sflow agents can be configured using the DNS-SD (DNS Server Discovery) protocol. DNS (Domain Name System) client functionality is universally supported on servers and DNS-SD is a method of using DNS to perform server discovery and distribute configuration information.

    Using DNS-SD, configuring all the servers in the data center is as simple as adding a few lines of text to the site's DNS zone file. The centrally managed configuration is then distributed to all the servers using DNS.

    The following DNS configuration settings instruct all the servers to poll counters every 20 seconds, sending sFlow to two sFlow analyzers, server and chow:

    _sflow._udp SRV 0 0 6343 server
    _sflow._udp SRV 0 0 6343 chow
    _sflow._udp TXT (

    In addition to providing a simple way to configure sFlow on servers, DNS-SD offers an attractive alternative to using CLI or SNMP to configure sFlow, particularly in data centers. DNS-SD offers a simple way to configure all sFlow agents in the physical network (see Multi-vendor support), virtual network (see Open vSwitch and Virtual routing), servers (see Cluster performance and Top servers) and virtual servers (see Host sFlow) in a coordinated and scalable way.

    Saturday, June 12, 2010

    Application mapping

    Understanding the complex relationships between applications and the server, network and storage resources on which they depend is critical for effective management. Keeping track of these relationships is particularly challenging in converged data center environments where virtual machine migration, scale out storage and elastic service pools create large scale, rapidly changing relationships between the application components.

    Current application discover and dependency mapping tools often require considerable manual configuration effort and can quickly fall behind in dynamic environments. Stale or incomplete dependency maps are of limited value in supporting the real-time performance, security and trouble shooting tasks that challenge data center managers.

    Scalable, real-time visibility into network, system and storage relationships is one of the benefits of adopting the sFlow standard for converged data center monitoring. Most switch vendors implement sFlow in their switch hardware, providing integrated, wire-speed visibility into traffic between servers, throughout the data center, without the need for agents (see Hybrid server monitoring).

    The application dependency map shown at the top of this page tracks application dependencies in real time using sFlow data (see Choosing an sFlow analyzer). The dependency map is only a small part of the integrated data center visibility provided by sFlow. The sFlow standard integrates network, storage and server monitoring to deliver a seamless picture of data center performance.

    Saturday, June 5, 2010


    The Fiber Channel over Ethernet (FCoE) protocol provides a method of carrying Storage Area Network (SAN) traffic over a switched Ethernet network. FCoE adds to the list of options for converged storage and data networking (see Networked storage) that provide the flexibility needed to support virtualization and cloud computing.

    Network visibility is critical for managing performance in a converged network. The sFlow standard embeds monitoring in Ethernet switches and provides visibility into all types of traffic flowing over the converged network (see Packet headers), including new protocols such as FCoE. The chart at the top of this page was created using sFlow data from a switch and shows a real-time view of FCoE traffic flowing through the switch (see Choosing an sFlow analyzer).

    Most data center switch vendors already support the sFlow standard. Selecting switches with sFlow support provides the visibility needed for effective management and control of a converged network.