You’ve probably heard “nines” thrown around when talking high availability, so let’s review them to make everyone talk the same talk or IT Jibba-Jabba.
These are used to show the uptime of a system. You basically track how many hours your system was available. Now, it doesn’t have to be 24/7, it can be availability during business working hours. As always with math, there are ways to manipulate the results.
For example, I have a one nine availability as I am in training, vacation, or in meetings. A mid-sized company probably has two nines as snow storms or electrical power outages can take HQ out of business. Five nines is what datacenters aspire to.
Anyway, why do you need to know this? Well, if I am comparing a car to another car with regards to safety, I need a metric. How else will I know if my baby is safe?
Normally, you would assume bigger is better. Take, for example, this Ford Ranger.
Basically, the pedals will bend into your thighs, your head will bang the steering wheel in spite of the airbag and your chest will collapse on the dashboard. Otherwise known as FAIL.
You may not be getting a hot date, but you will be making it home after crashing into a tree.
So what is my goal with all these examples? When you’re comparing two datacenters, you should use this parameter. What is our availability in NINES and what can we guarantee in writing?
If all you can be guaranteed is a car that has a one nine uptime, you might as well take the bus (cloud). So, how do you increase your uptime?
If you have one WAN connection to the internet, even if it is 10 Gbps, and someone does construction on the road next door, there goes your availability.
Their power is built into the switch. So if the power supply dies, you’ll lose at least an hour of downtime if you are in NY. Now if your datacenter is in the boonies, I’d factor in more hours. So buying a 3560/3750G will mean you will probably won’t make it to the four nines (59 minutes).
Anything critical should be on two power supplies or you can keep a cold spare switch at his office. That might cut your downtime to 20 minutes.
All real datacenters of repute strive for Five Nines. All switches have Dual power. One power goes on one grid, one power goes on another grid. If you recall Storm Sandy, if you don’t have two grids, well don’t complain if you drop down to one nine.
So to make an informed choice, ask yourself: what kind of UPTIME do you have to live up to? Are you contractually required to provide this uptime?
Based on the uptime or level of nines, you can know which equipment you need. For example, a 5 nines would be better off with an MX 480 since it has redundant routing engines while a 4 nines would be better off with an MX80 running as a pair. A 3 nines would be well served with a same day JCARE, while a 2 nines will manage fine with a NBD next business day. A one nine is usually someone who has simply not tallied the cost of downtime up and is blinded by “paying” less.
So, if you have any questions on the nines let us know. There are nines in every field in IT. From the disk drives (you use RAID to get higher nines), switches (you use dual powers and supervisors/routing engines), power (you use UPSs or redundant grids), and Wi-Fi (redundant controllers).
Saar Harel is a resident Engineer at Myriad Supply, and has been in the Networking Field for over 20 years. You can check out his Google+ and ask him questions!