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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">+1 Yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I had to refit a rack recently from a power rail of Australian standard AS/NZS 3112 (Type I), to the standard computer plug (can’t remember the standard).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">It was really easy because most of our equipment was dual railed.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The equipment that wasn’t had redundant devices… So dual attach to peering, ESX cluster etc etc.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Good HA/BCP also gives you more options….<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Alex<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> AusNOG [mailto:ausnog-bounces@lists.ausnog.net]
<b>On Behalf Of </b>Paul Gear<br>
<b>Sent:</b> Thursday, 24 April 2014 11:31 AM<br>
<b>To:</b> ausnog@lists.ausnog.net<br>
<b>Subject:</b> Re: [AusNOG] Question about hardware spec for a DC<o:p></o:p></span></p>
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<p class="MsoNormal">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:<o:p></o:p></p>
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<p class="MsoNormal">IMHO <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Read up on HA concepts if you're not sure what you need or why.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">13 years old now but this book is still handy and the concepts still hold true,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><a href="http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175">http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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