Brian Nicol Education

DR101: RPO & RTO Explained

Disaster Recovery isn’t just about protection from natural disasters. It’s about ensuring that whatever happens to your infrastructure, you won’t suffer extended downtime.

RPO (Recovery Point Objective)
The last point-in-time that IT systems and applications can be recovered to. RPO is dictated by the replication Technology used.
Backups, Storage Replication, Continuous Data Replication

RTO (Recovery Time Objective)
How quickly applications are recovered and operations are resumed. RTO is influenced by the level of manual vs automated recovery processes.
Boot Ordering of VMs, Re-directing Network Traffic, Recovering Application Stacks Consistently

Brian Nicol Uncategorized

Test Mail Server for Inbound TLS

Here’s how to test if a mail server supports TLS using a windows pc:

  1. nslookup
    > set q=mx
    > google.com
  2. The results:
    google.com   MX preference = 100, mail exchanger = google.com.s9a1.psmtp.com
    google.com   MX preference = 300, mail exchanger = google.com.s9b1.psmtp.com
    google.com   MX preference = 200, mail exchanger = google.com.s9a2.psmtp.com
    google.com   MX preference = 400, mail exchanger = google.com.s9b2.psmtp.com
  3. > exit
  4. telnet google.com.s9a1.psmtp.com 25
  5. After connected type:
    ehlo google.com
  6. If you see this in the output, the mail server supports inbound TLS communication:
    250-STARTTLS
Brian Nicol Uncategorized

Understanding the “Nines of Availability”

If you’ve spent any amount of time in the tech field you’ve probably heard of the “Nines of Availability”. Availability is usually expressed as a percentage of uptime in a given year. The following table shows the downtime that will be allowed for a particular percentage of availability, presuming that the system is required to operate continuously.

Availability %Downtime per yearDowntime per monthDowntime per week
90%36.5 days72 hours16.8 hours
99%3.65 days7.20 hours1.68 hours
99.9% (“three nines”)8.76 hours43.2 minutes10.1 minutes
99.99% (“four nines”)52.6 minutes4.32 minutes1.01 minutes
99.999% (“five nines”)5.26 minutes25.9 seconds6.05 seconds
99.9999% (“six nines”)31.5 seconds2.59 seconds0.605 seconds
Brian Nicol Education, Support

How to ask for help!

During my career I have run into support issues where I needed additional help and I had difficulty asking for that help. Soon I realized that most successful people know how and when to ask for help. And most people are inclined to offer help when asked (research backs this up.)

Based on these experiences, I’ve developed some guidelines for how I ask for help:

Identify the problem. This might sound simple, but it’s not.

Learn as much as you can on your own.  Do your own research! Some support issues are so common a simple Internet search can yield a resolution.

Make it easy. Based on the research, perform some preliminary diagnostics which can yield a resolution.

Be clear. If the preliminary diagnostics does not yield a resolution, it’s time to ask for help. During your conversation with the helper, be clear and in great detail describe your issue, research, and preliminary diagnostics preformed.