I would have to agree with the other post a mixture of different devices for management is the way to go. In our infrastructure we rely havily on HP Openview for network node management, along with cisco works and a tonne of other tool set's that perform various functions within our environment. Thse tool set's all run from various servers for flexability and management.
Appliances are great for reducing load on a server to perform it's given tasks (ie, what it is designed to do) but with a server approach you have greater flexability to scale your needs upwards without having to roll out a new piece of hardware (in most cases) to support the software. As is the case with an appliance approach if you want more you need to scale up the hardware to accomodate the features which usually means a drastic increase with Price. Either Case both approachs do provide real-time or near real-time metrics depending on what your configuring or wanting to manage
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