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
