Skip to main content

Newbie datacenter lesson: The implications of 120v and 220v

So I've never initiated a fresh colo build before, and it's showing.  And before you get all pedantic, I know 220v is probably not the right term (208, 240, etc), but it's what I'm using.  So there.  Newbie, right?

Problem: Not getting super specific about what our power circuit will be.

Assumptions by both parties caused this, but the fault really only matters on my side.  It ended up being that I ordered the wrong PDUs (well, right if you assumed 220v), and moving to a 220v circuit would have been an additional monthly cost.  I incorrectly assumed that we would be getting a 220v/20A circuit.
  • The difference between 120v/20A and 220v/20A is significant
  • The difference between L5-20 and L6-20 is significant
  • The difference between 20A and 30A is significant
Let's address these, because it's been a heck of a learning experience for me.

120v and 220v

Why is it a big deal?  To sum it up really quickly - 220v basically means you can house twice the equipment.  
  • Amps = Watts/voltage
  • get the amps of a 750w power supply, you take 750, divide by 120, and bam: 6.25A
  • Using 220v: 3.4A
So that minor difference in numbers (120 vs. 220) means you're in an awkward position if you've done power calcs based on 220v input and they give you 120v.

Another gotcha is the thought 'no biggie, just upgrade to 220v!'.  Well, now you need new PDUs.  Congratulations.

L5-20 and L6-20

If you look up the wikipedia page for NEMA standards, the key difference between L5 and L6 is voltage. L5 is 120v, L6 is 220v.  Plus, they are physically incompatible (because magic smoke).  What this adds up to is buying a PDU with an L6 plug means you are sending it back when you discover you've been given an L5-20R to connect to.

We bought some fancy APC metered/switched AP8659NA3 PDUs, but now they're going back because they are 220v only.

20A and 30A

This is less siginificant, but still an issue.  When you buy a PDU, you have to specify plug type, plus max amperage.  So you've bought a PDU rated for 20A, and you upgrade circuits to 30A - now your PDU is the limiting factor.

Side notes

20A is actually 16A.  So if your power calcs come out to 16A and you're all 'phew, 75%!'...wrong - 100%!  For whatever reason, a 20A circuit in North America is actually specified as 16A maximum.

Also fun - while your Dell iDRAC will tell you actual power consumption, your much more expensive EqualLogic array has no capability to do this (as of Jan, 2015, anyways).  The solution for those without nice metered PDUs?  Kill-a-watt.  Yep - sanctioned by EqualLogic support, even!

For a full rack (assuming you're not just storing paper and hot air in it), I simply cannot see how you can get away with 120v/20A.  My middle-of-the-road calcs for 6x R620s, 1x PS6510, 1x PS4210, and networking gear comes out to 12A.  Remember, 12A out of a max of 16A!!  That's a 75% load right there...and we're only talking about 24U of equipment!

So yeah.  Pay attention to power specs.  Important stuff to get right from the start.


Popular posts from this blog

DFSR - eventid 4312 - replication just won't work

This warning isn't documented that well on the googles, so here's some google fodder:

You are trying to set up replication for a DFS folder (no existing replication)Source server is 2008R2, 'branch office' server is 2012R2 (I'm moving all our infra to 2012R2)You have no issues getting replication configuredYou see the DFSR folders get created on the other end, but nothing stagesFinally you get EventID 4312:
The DFS Replication service failed to get folder information when walking the file system on a journal wrap or loss recovery due to repeated sharing violations encountered on a folder. The service cannot replicate the folder and files in that folder until the sharing violation is resolved.  Additional Information:  Folder: F:\Users$\\Desktop\Random Folder Name\  Replicated Folder Root: F:\Users$  File ID: {00000000-0000-0000-0000-000000000000}-v0  Replicated Folder Name: Users  Replicated Folder ID: 33F0449D-5E67-4DA1-99AC-681B5BACC7E5  Replication Group…

Fixing duplicate SPNs (service principal name)

This is a pretty handy thing to know:

SPNs are used when a specific service/daemon uses Kerberos to authenticate against AD. They map a specific service, port, and object together with this convention: class/host:port/name

If you use a computer object to auth (such as local service):

If you use a user object to auth (such as a service account, or admin account):

Why do we care about duplicate SPNs? If you have two entries trying to auth using the same Kerberos ticket (I think that's right...), they will conflict, and cause errors and service failures.

To check for duplicate SPNs:
The command "setspn.exe -X

C:\Windows\system32>setspn -X
Processing entry 7
MSSQLSvc/ is registered on these accounts:
CN=SQL Admin,OU=service accounts,OU=resources,DC=company,DC=local

found 1 groups of duplicate SPNs. (truncated/sanitized)

Note that y…

Logstash to Nagios - alerting based on Windows Event ID

This took way longer than it should have to get here's a config and brain dump...

You want to have a central place to analyze Windows Event/IIS/local application logs, alert off specific events, alert off specific situations.  You don't have the budget for a boxed solution.  You want pretty graphs.  You don't particularly care about individual server states.  (see rationale below - although you certainly have all the tools here to care, I haven't provided that configuration)

ELK stack, OMD, NXlog agent, and Rsyslog.  The premise here is as follows:

Event generated on server into EventLogNXlog ships to Logstash inputLogstash filter adds fields and tags to specified eventsLogstash output sends to a passive Nagios service via the Nagios NSCA outputThe passive service on Nagios (Check_MK c/o OMD) does its thing w. alerting
Open Monitoring Distribution, but the real point here is Check_MK (IIRC Icinga uses this...).  It makes Nagios easy to use and main…