bsdinstall misaligns partitions
Warren Block
wblock at wonkity.com
Fri Jan 4 21:30:46 UTC 2013
On Fri, 4 Jan 2013, Christian Weisgerber wrote:
> Shouldn't bsdinstall attempt to align partitions on 4k boundaries
> both for the benefit of 4k drives and flash storage?
I think the latest version does.
> I just installed 9.1R i386 for fun and practice, in fact I installed
> it several times, and I played around with the partitioning options.
>
> * The modern GPT scheme reserves 34 sectors at the start of the disk.
> Your newly created partitions will start at offset 34 and will
> therefor be misaligned. I ended up configuring a 63 kB freebsd-boot
> partition, which ensures that the following partitions are aligned.
>
> * The old MBR scheme is even worse. The FreeBSD slice will start
> at sector 63, guaranteeing that any partitions contained within
> will be misaligned. There is no way to fix this, unless you
> shell out and run fdisk manually.
Even worse news: you can't fix it manually. Both fdisk and gpart are
slaves to the kernel code that deals with MBR layouts, and will align to
the old CHS values. I have not found a way to use FreeBSD to create an
MBR slice that starts at 1M, block 2048. The CHS alignment always
forces it to block 2079, a multiple of 63.
However, gpart's -a alignment flag will offset BSD partitions within the
slice so they are aligned.
> * Funnily enough, the ancient BSD "dangerously dedicated" scheme
> is the only one that out of the box does not misalign partitions.
The filesystems don't begin at the start of the slice anyway. There is
a bsdlabel there.
> I'm presumably not the first one to notice this issue, and yes, I'm
> mostly just venting.
A way to override the CHS alignment would be welcome.
More information about the freebsd-questions
mailing list