One of the things that may affect any clusters you have – or other systems – is that management does not want to spend enough to handle any possible load. With a cluster, this means that you may not be able to handle a fail-over because there is not enough spare processing power to handle the extra load when it happens.
HP’s Instant Capacity (“capacity on demand”) is an answer to this dilemma. The base idea is that you have extra hardware already in the data center that is not available for use until it is necessary. The switch that will enable this expanded capacity can be automatic or manual; when some portion of the extra capacity is enabled, you pay for it and it can be used from then on.
Yet, Instant Capacity (iCAP) is more flexible than this. The capacity may be enabled only temporarily instead of permanently – this is known as TiCAP (temporary iCAP). Thus, you can save even more by buying extra hardware but enabling only a small portion of it. During the recent HP Tech Days that I attended in San Jose, California, a situation was described where an HP Superdome could be purchased with a large amount of the hardware already in place – but only a small amount of the hardware enabled. When the extra power is needed, for example, a cell in the Superdome could be enabled until such time as the power is no longer necessary.
There is also Global Instant Capacity (GiCAP) which even allows the movement of power from one system to another. For example, if a CPU on one system is underutilized and another system needs the resource more – then the CPU resource can be “logically” moved from one system to the other through GiCAP. Alternately, if one system dies and another system needs its power, the dead system’s resources can be used by the active system by moving them through GiCAP.
iCAP and TiCAP are available for HP-UX (on PARISC and Itanium) and for OpenVMS (only on Itanium). GiCAP is only available for HP-UX.
I find iCAP and TiCAP to be very interesting. From a cost perspective, you pay only a minimal amount to keep the resource; when it is enabled, you then pay for it for the duration – or buy the hardware outright for permanent use as needed.
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