Wednesday, August 12, 2009

SQL Quiz 5: SANs Mirroring

My turn to answer Chris Shaw’s questions “Do I feel I have a reliable SAN solution?” and “Describe Database Mirroring for the layman?” Thanks Grant for tagging me. More important to me than the sharing of knowledge, is the building the community through our interactions. Besides, I'm not an expert or even novice in these subjects. So be forewarned before proceeding.

I recall in the beginning of my DBA career, a Database server was a box I could see, touch and if necessary, kick. One day, it became a smaller box that was in a backroom somewhere, in a 'rack'. With access to this special room, I could still kick it. Now, we use SANS. What the heck are these things? I don't have access to them. I can't see them. I cant even find the room where they are at. I'm definitely no longer allowed to kick them.
Now we have to go through folk with magic fingers and pixie dust to get some space for a db server. They do all kinds of things that I don't understand. But if they do it right, I get an IP address or name of a DB server, and its so much better than it used to be, with much more stuffs than I could ever hope for previously. Tons of space, and it's uptime is so much better. When something does break, its usually not the DBA's fault. Like when converting from generator power to real power, and forgetting to connect the SAN your standby topology is on at the same time. Fun stuff! But I do miss the days I could walk into a room and kick my DB server and it was all in 1 box. Mainly I liked to see it sitting there and often, kick it.

Many years ago, in the beginning of our marriage, we went to a car dealer. They had a special on two cars at the time. We almost bought them both, and would have had two identical cars. If we kept them both tuned and in good working order, I could go out in the morning and take one of them. If something happened to that one, I could take the other, and not really notice the difference. My tasks would still be accomplished in the same way, and if I didn't pay close attention, I'd be none the wiser.
This is how I imagine mirroring functions. There are two dbs out there, that are identical. Something keeps them running the same. If one has an issue, we start using the other. Quite magically. You, the end user, simply gets in the DB, and drives off, returns it to its parking space, and viola, repeats when necessary.
You don't need to know that behind the curtain there are any number of processes, people and other stuffs switching things out, configuring things, setting things up, and so on. What you see is a functioning item on your side of the fence, and its available when you need it.

To sum this all up in my own words wouldn't be as much fun as realizing my conclusion is the same as Grant's. So to plagiarize Grant, "So to sum up, the answer to both questions is, I don’t know. Pretty pathetic, but honest." -Grant Fritchey

Now tagging Pat Wright and Andy Leonard.

No comments: