Well, that could have gone better

I volunteered to give a presentation to Linux Users Group of Rochester (LUGOR) about LVM, the Logical Volume Manager. I knew I had half an hour, and so I made a presentation, rehearsed it several times, and knew I could go through it in half an hour. I did it on my laptop, using VirtualBox to stand in for a computer that I could virtually add and remove drives from. I was told the room we were presenting had a projector that took HDMI input, and my laptop has an HDMI output, so I figured I was set.

First hitch was arriving to find out that we had been bumped from our room because some musicians were warming up for a concert they were giving elsewhere in the building, and the new room had a projector that only took VGA or DVI. Oh, and also I’d evidently gotten my signals crossed and I was really supposed to present next month. But no mind, the guy who was supposed to give the second talk today wanted to go first because he was sick and wanted to bail early, and the guy who was supposed to give the first talk wanted an hour not half an hour and would rather postpone. So the guy who wanted to go first talked first, and got me all intrigued about “ownCloud”. I may be setting that up one of these days.

Then the first room became available again, and we trooped back to it. And then I plugged in my laptop, got the two screens non-mirrored all set up so I could do the Powerpoint presentation part of the show, and then the projector screen started randomly flashing between what it was supposed to be showing and a green screen with something about HDCP displayed on it. I didn’t know it at the time, but that means that the copy protection stuff on my laptop isn’t compatible with the copy protection stuff on the projector. We spent some time trying to wiggle wires, change settings on both the laptop and the projector, etc, and finally I gave up.

Another guy gave a good quick little presentation on the Raspberry Pi. Amazing power in such a small cheap package. I’ve got one on order for another project, but it might be many weeks before I see it.

While he was talking, one of the other members handed over his laptop. It was an Acer that isn’t as high end as my MacBook Air, but it had two things going for it:

  1. It had already proven it could display to the projector, and
  2. It had VirtualBox installed on it.

I copied my VirtualBox disk files and my PowerPoint over to his laptop, and when the Raspberry Pi presentation was over, I started my presentation. And that’s when the next problem reared its ugly head. Every time I booted my VirtualBox instance on my laptop, it takes about 10 seconds or so. Every time I booted it on his computer, it took literally 10 minutes or more. Since I had to reboot several times in the presentation (because I was simulating adding and removing disks), this caused the presentation to drag out drastically. Fortunately there were lots of things to talk about during those long pauses. Charles, the organizer, used one of the pauses to explain in great detail what exactly I was doing with the VirtualBox and which parts of what I was showing belonged to it and which belonged to the guest OS and which belonged to LVM, something which I fear I hadn’t even though to explain in my presentation. With all the long pauses and delays, my “30 minute talk” ended up being somewhere between an hour and an hour and a half. And worse still, on the very last boot of my talk, I discovered that if I increased the number of virtual CPUs from 1 to 4 the boot went much, much faster. I’d only ever used 1 virtual CPU on my own laptop and hadn’t noticed any problem – I don’t know if that’s a difference between my i7 processor and the loaner laptop’s i5, or because mine is hosted on OSX and his is hosted on Linux. I wish I’d discovered this earlier in the talk, though.

If you care, slides are available at https://www.dropbox.com/sh/y4822v4k6am0s9s/IFhrMz-HEW/lvm.pptx but probably not for too long.