Get DB sums with Powershell

Here’s a cute little piece of code to add up the sizes of all your DBs on a server.  It comes in handy when you’re trying to see how much space you’ll need to duplicate the server either for DR, or reporting, or even just to see how much backup space you’ll need.

Make sure you’re at the DB context of PS:


Then type this code:

>dir | %{$Total += $_.size}


Ok, that’s it.  Not too bad, huh?  Now, let’s work on making it look like something you can actually work with. 

Ordinarily you would prettify this by just dividing it by the measure you want to convert it to.  So if you wanted to convert it to GB, then that would look like this:


However, you can’t do that here.  Here’s what you need to know.

This output is in MB, and the “/1GB” trick assumes that the output is in bytes.  So lets assume that your $Total is 4189811.4375.  Remember now, that’s in MB.  So here’s what the 1GB trick will yield.



That’s not even close to right.  And again, that’s because the 1GB trick assumes your output will be in bytes.  So here the best way to convert this to GB is to do the math yourself like this:



Of course, you can still use one of the tricks to get the number you’re looking for, but since you’re already in MB you have to go 1 measure down to make it come out right. 



So why is that?  Well, because 1KB is only a shortcut for 1024, and from MB, the conversion to GB is /1024.  And the problem of course with doing it this way is that it’s deceiving as hell.  Anyone else looking at this will think you’ve converted to KB because they may not realize that the original output is in MB.  So don’t use this one, I only threw it in there to show you how to come up with the right number.  It also shows you something about how the trick works.

Now, you can still use the 1GB trick, you just have to massage the data first.  So here we’re going to put it back into bytes and then convert it to GB.  This is really just to prove to you that the output for this trick really is assumed to be in bytes.



Personally I’d never do it this way.  Sure, it shows you and someone else what’s going on so you can read the code, but that’s also what comments are for.

>$Total/1024 # Convert to GB.  Can’t use /1GB because this output is in MB and the /1GB assumes the output to be in bytes.

See, what’s wrong with comments?

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