165 Halsey recurring power issues

Wed Nov 1 02:51:13 UTC 2023

Willing to bet that there was slicing on both sides of that conversation 
and this is what I will now refer to as the expected and resulting razor 
burn.

Babak Pasdar wrote:
> Thanks James,
>
> At signup we asked for N+1 power, two circuits to different UPS units. 
> I think they sliced it thin by connecting us to two battery packs on 
> the same UPS. When the UPS controller crashed both battery packs went 
> down.  Which now raises the question -- is it reasonable to have to 
> specify and expect that two UPS units means that they do not share any 
> common points of failure.
>
> Is the UPS the battery or the battery and controller combined?
>
> Babak
>
>
>
> On 10/23/23 15:16, James Jun wrote:
>> On Mon, Oct 23, 2023 at 10:38:09AM -0400, Babak Pasdar wrote:
>>> I wanted to get some feedback as to what is considered standard A/B
>>> power setup when data centers sell redundant power.?? It has always 
>>> been
>>> my understanding that A/B power means individually unique and 
>>> preferably
>>> alternate path connections to disparate UPS units.
>> Generally speaking, the definition of A/B has become muddied in 
>> recent decades.  It has almost become an inaccurate marketing term.
>>
>> Most sane people have the opinion (myself included) that when "A/B" 
>> power is offered, it is at minimum offererd as 2N UPS (different 
>> building entrance and MSBs and even physically separate UPS rooms are 
>> also desired on a true 2N A/B, but may not always be available).  
>> Some data center operators go even further and architect load 
>> switching within their distribution, thereby preventing 
>> single-side/one-leg power outages for customers during most of their 
>> power maintenance activities
>>
>> Some data center operators treat "A/B" as convenience for them to 
>> undertake maintenance and offload uptime responsibilities to their 
>> own customers, and require them to either undertake their own 
>> transfer switching and/or dual-cord every equipment, so that they can 
>> keep taking one side of the power system down for repeated 
>> maintenance.  This does not scale well for retail colo, as not every 
>> customer is going to be good at maintaining two PSUs for every single 
>> piece of equipment.
>>
>> Some data centers also view "N+1" system deployment at the UPS as an 
>> acceptable form of A/B protection, as long as customer circuits are 
>> on different PDUs.
>>
>> Long story short, whether you're receiving N+1 or 2N or 1N, it's 
>> important to inquire about how your power circuits will be 
>> architected and delivered by the data center, and either have that 
>> codified in the contract or reflected appropriately in SLA offering.  
>> There is nothing wrong with the data center providing N+1 or 1N 
>> power, as long as they're transparent about it and that it is what 
>> you're willing to accept for the right terms. However, simply 
>> accepting "we are providing you A/B power" or "we've never had 
>> primary power failure" are not sufficient to meet proper due 
>> diligence during a site selection process, unless you can accept the 
>> site outage occurring from time to time, or you're deploying your own 
>> power plant (i.e. DC power and batteries) to supplant data center's 
>> own power protection scheme.
>>
>> James
>
>