The Worst Way to Judge SQL Server’s HA/DR Features

We love to help people plan for disasters

We’re not pessimists, we’ve just seen one too many servers go belly up in the middle of the night to think that having only one is a good idea. When people ask us to help them, we have to take a lot into consideration. The first words out of the gate are almost always “we’ve been thinking about Availability Groups”, or some bastardized acronym thereof.

Don’t get me wrong, they’re a fine thing to think about, but the problem is that usually people’s only exposure to them, if they have any exposure to them outside of thinking about them, is just in setting them up.

Usually with VMs.

On their laptop.

With a few small test databases that they just created.

And they’re really easy to set up! Heck, even I can do it.

But this is the worst way to judge how well a solution fits your team’s abilities.

Everything’s easy when it’s working

When things get hard, and when most people figure out they’re in way over their heads, is when something goes wrong. Things always wait to go wrong until you’re in production. In other words, driving a car is a lot easier than fixing a car.

If you don’t have 2-3 people who are invested mainly in the health and well-being of your Availability Groups, practicing disaster scenarios, failing over, failing back, and everything in between, you’re going to really start hating the choice you made when something goes bump in the night.

And stuff goes wrong all the time. That’s why you wanted HA/DR in the first place, right?

Stuff can go wrong when patching

I mean, REALLY wrong

Sometimes index tuning can be a pain in the neck

You need to think before you fail over

Setting them up isn’t the end of the line

Fine, don’t believe me

Play to your strengths

If you’re a team of developers, a lone accidental DBA, or simply a few infrastructure folks who don’t spend their time reading KB articles on SQL and Windows patches, testing those patches in a staging environment, and then pushing your app workload on those patches, you’re going to have a tough time.

Things that are still great:

No, you don’t get all the readable replica glamour, and the databases failing over together glitz, but you also don’t get to find out you’re the first person to Google the error your Availability Group started throwing at 2am, shortly before you, your app, and all your users stopped being able to connect to it.

Try scaling up first

If part of your move to Availability Groups is Enterprise licensing, get some really fast CPUs, and enough RAM to cache all or most of your data. You may not need to offload the stuff that’s currently a headache.

Try some optimism

Optimistic isolation levels like RCSI and SI can help relieve some of the burden from large reporting queries running over your OLTP tables.

Get your script on

No, I don’t mean getting your baby mama’s name tattooed on your neck. I mean scripting out parts of failing over Mirroring or Log Shipping so that it’s not such a bleary-eyed, manual process. Availability Groups don’t keep agent jobs, users, and other custom settings synced from server to server, so you’re going to have to figure that part out anyway.

Still interested in coming up with a HA/DR solution that works for you? Drop us a line!

Thanks for reading!

Doug says: And remember folks, HA/DR solutions sometimes differ between on-premises and cloud. Make sure the cloud features you want to use are fully supported.

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3 Comments. Leave new

  • Everything is always easier when you read about it online lol. All I can say is long days and night.

  • I’m in the process of redesigning our SQL infrastructure. As far as my SQL team, well, there isn’t an “I” in team, but there is an “m” and an “e”, and “me” is it. So I was leaning towards something a little easier like mirroring. However, in looking at the Microsoft site, their take on it for 2014 is:

    Database mirroring
    This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. We recommend that you use AlwaysOn Availability Groups instead.

    So does that leave small shops like ours with Log Shipping or Availability Groups, or is going with mirroring and crossing that bridge when we come to it a reasonable strategy?

    • Erik Darling
      June 22, 2016 12:46 pm

      Mirroring is still supported as of 2016, so it hasn’t been moved out yet. I’d say it’s still viable, because by the time it IS removed from the product, and you’re planning a major version upgrade, AGs might be usable by a single human being who doesn’t sleep with a pile of SQL Server books on their stomach like Edgar Cayce.


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