On Fri, Mar 11, 2011 at 02:26:56AM +0100, Markus Schatzl wrote: > Thanks Otto, > > this is somehow obvious, nevertheless there are tools relying on the > partition layout, like disklabel (at least regarding the start of the > partition).
Well, we are slowly moving away from any CHS considerations in disklabel. For various reasons it is not yet possible to completely do away with CHS in all cases. But for most purposes and with LBA capable disks, you can use ANY offset. Just put in sector numbers, in that case they are not rounded to cylinder boundaries. > So essentially, every start above the first sector (ie. the MBR) would be > acceptable? I see that the installer suggests sector 2 as start of the > disk (in fdisk), however disklabel starts wd0a at offset 64 (default), > which seems kind of odd. Is there an explanation for this effect? You want to leave some room for things like alternative boot loaders and who knows. Skipping the first track is a safe practice. We used to start at the 2nd track (offset 63 in most cases) but that has been moved to 64 to accomodate 4k block disks. > > Amit: You're right. However, as disks from about 2005 onwards are larger > than this boundary, you always can _accidentally_ choose to make your boot > partition too big. As the C/H/S configuration is kind of an advanced > option, I'd believe in a healthy common sense of people using this option, > instead of preventing them to accomplish the task they're after. I don't think Amit is right, we are able to boot from any offset with an LBA capable disk on i386 and amd64. Some bioses have limitations, as is explained in the FAQ: http://www.openbsd.org/faq/faq14.html#LargeDrive It is amazing how old limitations tend to stick into the collective memory, despite all the work done to overcome the limitations. -Otto
