Aligning MBR for ZFS boot help
Warren Block
wblock at wonkity.com
Mon Mar 11 00:39:33 UTC 2013
On Sun, 10 Mar 2013, Dennis Glatting wrote:
> Sorry for the stupid question but is this issue (and issues) and
> procedures written up somewhere?
The wiki shows using GPT:
https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/9.0-RELEASE
The issue with MBR is that FreeBSD strictly follows the standard of
alignment to CHS values. However, for the last couple of decades,
drives have used variable geometry to fit more data on the outside
tracks, so CHS values don't apply any more. Combine this with the new
need to align MBR slices to particular values of 4K or 1M, and FreeBSD
has a problem.
Solution: use GPT when possible. But some systems won't boot from GPT.
If MBR partitioning is required, and alignment is needed, use some other
operating system to create the MBR, and don't try to edit the slices on
FreeBSD.
I don't know if anyone has documented all this in one place. If FreeBSD
had a way to turn off the strict enforcement of CHS values for MBR, it
would make that unnecessary.
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