On 9/19/25 12:12, Roderick wrote:
Are there (dis)advantages of UEFI over BIOS on an installation?
yes -- but it's 100% a hardware issue. Some hardware doesn't support UEFI, some hardware doesn't support BIOS/MBR. Some hardware supports both, but one or the other is buggy. Some hardware supports both, but one or the other works better with OpenBSD. yes, I've seen HW that was sold as a linux device (HP thin clients) that /required/ using MBR/BIOS for Linux, but /required/ EFI to work with OpenBSD properly.
I need the computer only for desktop with OpenBSD, no 24h server.
no impact on the decision process there.
By the way, are there restriction on the size of root / its position in the HDD?
On modern hardware, that pretty much says "doing it wrong". Don't make a mega-root partition system. In all cases, the system firmware is what loads the kernel, so the system firmware has to understand how to access the disk where the kernel resides. IF you had a really old 486 that had enough memory and you put a 500GB disk on it, you might find that the system couldn't load the kernel beyond 8GB or even 504MB. That sets an upper limit to the size of your root partition (other common limits were 2G, 32G, 40G (yeah, pretty sure that was a buggy BIOS). Of course, once the kernel has loaded from the root partition, limitations of the system firmware no longer apply. But don't make a giant root partition. As for disk limits, there are a number of OSs that restrict the accessible disk size to 2T for MBR. OpenBSD is NOT one of them. You absolutely can have as big a disk as you can find, and still have it be MBR. OpenBSD uses the MBR (and EFI) partitions just to mark off the space the OS requires; the disklabel is what defines OS file systems for OpenBSD, and that supports very large disks.
Are there recommendations?
The primary criteria I use for deciding between MBR and EFI are: 1) what does the hardware require to run properly? 2) What will the REPLACEMENT hardware require to run properly? At some point, I assume every part of the existing system will have to be replaced, either by necessity (failure) or getting better hardware. I'd assume any replacement system will be better performance and probably newer than the old system, and these days, that basically means EFI is a "safer" choice. Yes, today's hardware may run MBR just fine, but tomorrow's may not. MBR is very definitely legacy now. Lots of words for what really boils down to a simple answer: use EFI if at all possible. And if it isn't...reconsider your life choices. :) Nick.
