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<div class="moz-cite-prefix">In my judgement, the big benefit of
dual power supplies (particularly on servers, switches, &
routers) is that it enables reorganising of power circuits in
racks without requiring a downtime window. Like you say, a
comprehensive view of high availability means designing N + 1
redundancy at the system level, but dual power supplies to those N
+ 1 devices is a big convenience factor.<br>
<br>
Paul<br>
<br>
On 04/24/2014 11:25 AM, Colin Stubbs wrote:<br>
</div>
<blockquote
cite="mid:CA+CbT+vqH4QhXpsneX3LVmVK1C01TYAZZpGJPw9hxbGnPAcJMw@mail.gmail.com"
type="cite">
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<div dir="ltr">IMHO
<div><br>
<div>Avoid that auto power-transfer stuff in rack if you can.
Those devices are best used only for low end boxes like
NTU's/etc with which you can only ever install/utilise a
single box at a time.</div>
<div><br>
</div>
<div>
<div>Buy equipment which has dual PSU's as an option in
preference, but don't mandate it or mandate buying the two
power supplies. Mandating it will just mean you're wasting
part of your budget unnecessarily on every single purchase
as you may force yourself to buy bigger boxes than
required; and/or buy more PSU's than you need.</div>
</div>
<div><br>
</div>
<div>Avoid *depending* on dual PSU's if you can, e.g. don't
design anything with the assumption having two power
supplies in a box will keep everything working if there is a
loss of power or if one of the PSU's fails.</div>
<div><br>
</div>
<div>Design for failure with N+1 redundancy at a system level,
e.g. install two or more of every box and use them in
active/active or active/standby capacities. If you do that
you won't necessarily require two power supplies in each to
achieve a very high level of availability.</div>
<div><br>
</div>
<div>Choose to use dual PSU's primarily based on the location
and the power infrastructure available, in combination with
how many boxes you have. e.g. if you're in a crappy DC where
they can't deliver access to two genuinely independent
sources of power the value of having two PSU's is greatly
reduced regardless of how many many boxes you've installed.</div>
<div><br>
</div>
<div>Read up on HA concepts if you're not sure what you need
or why.</div>
<div><br>
</div>
<div>13 years old now but this book is still handy and the
concepts still hold true,</div>
<div><br>
</div>
<div><a moz-do-not-send="true"
href="http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175">http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175</a><br>
</div>
<br>
</div>
</div>
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