As a general rule if the end customer was finance/bank their Linux flavor was RedHat (someone to yell at when it broke). Other tech companies / web types it was Ubuntu. This was my experience in over 4 startups where these were are end customers. Your mileage may vary.
Pretty much my exact experiences. Banking and large corporations: RedHat, because they buy support contracts to have guaranteed security and stability updates, and because they want some assurance that whatever (open/closed) corporate software they use will run on their Linux systems. Debian and especially Ubuntu the last years for smaller "dev" companies because the devs like to be close to the open-source ecosystem.
I've never met an individual (not corporate server) or end-user (desktop) running RHEL though.
Back to topic, I've been following Btrfs... At one point it seemed destined to become the default for most Linux systems, but I'm not sure where it is headed now.
CentOS is extremely popular among startups. It lets you directly use RPMs, which many software publishers distribute on their own (not the case for debs, often), and gives you an upgrade path to buy RHEL when you want someone to yell at and not throw away all your automation.
I’m not trying to start a flame war here (honest), but among most “usual web” ops folks I know, the opposite of what you’re suggesting seems to hold and Debian/Ubuntu are looked at as an odd choice. It’s probably hire #1 going with what they know, more than anything, and it could very well be selection bias regarding the people I know. I’d love to see stats.
I’ve been working with CentOS or OEL in my own roles for several years now, and I’ve never chosen it. (Not saying I wouldn’t, just that it’s been there when I get there.)
There are just as many publishers that supply debs and not rpms. It really depends on what you're after.
But if you look at the usage, north america is generally more redhat-family and europe is generally more debian-family, even in the SuSE patch that is Germany...
Oracle Linux is the only direct upgrade path for CentOS (afaik).
A full reinstall is required to move from CentOS to RHEL. Oracle has a procedure to directly convert CentOS, RHEL, and Scientific Linux into a supported Oracle Linux system.
KSplice is the most common reason why this conversion is required and mandated. If downtime can no longer be tolerated for upgrades to openssl/glibc/vmlinuz, this is the only available path.
In my experience Debian seems to be more common in Europe. Here there is a mix of RHEL, Debian, Ubuntu and some CentOS. With banks and finance preferring RHEL.
