<div dir="ltr"><div class="gmail_extra"><br></div><div class="gmail_extra">I once thought like that too.</div><div class="gmail_extra"><br></div><div class="gmail_extra">But if you're re-organising power and yanking cables out and plugging them back in on anything other than a lab system you should be working within a declared maintenance window anyway. </div>
<div class="gmail_extra"><br></div><div class="gmail_extra">There's too much risk that something will come out that shouldn't, or that something will shift just enough to cause a problem. </div><div class="gmail_extra">
<br></div><div class="gmail_extra">It might be acceptable to do it without a window for a UAT/test/dev system but anything revenue generating or revenue supporting... hell no.</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">
Having the convenience and ability to re-arrange power cables at any time of day without risk and loss of $'s stems from designing systems to cope with failure to start with.</div><div class="gmail_extra"><br></div><div class="gmail_extra">
That may in small part be because you put two PSU's in the boxes; but it won't be the only reason.</div><div class="gmail_extra"><br></div><div class="gmail_extra">-Colin<br><br><div class="gmail_quote">
On 24 April 2014 11:30, Paul Gear <span dir="ltr"><<a href="mailto:ausnog@libertysys.com.au" target="_blank">ausnog@libertysys.com.au</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>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.<span><font color="#888888"><br>
<br>
Paul</font></span><div><br>
<br>
On 04/24/2014 11:25 AM, Colin Stubbs wrote:<br>
</div></div><div>
<blockquote type="cite">
<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 href="http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175" target="_blank">http://www.ciscopress.com/store/high-availability-network-fundamentals-9781587130175</a><br>
</div>
<br>
</div>
</div>
</blockquote>
<br>
</div></div>
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