Aligning MBR for ZFS boot help
Warren Block
wblock at wonkity.com
Sun Mar 10 23:59:19 UTC 2013
On Sun, 10 Mar 2013, Adam Nowacki wrote:
> I don't think zfsboot is aware of BSD disklabel (offsets other than 0 won't
> boot). Is there any reason you are using BSD disklabel and not two partition
> MBR?
MBR slices created on FreeBSD are forced to CHS alignment, pretty much
always misaligned for 4K-block hard drives or SSDs.
> I also don't think there is any merit in aligning to 1MiB. Most ZFS IOs will
> be aligned to sector size (ashift). Unless ZFS pool is created with higher
> ashift then the 63 sector offset is as good as any.
If the drive has 4K sectors, that will be misaligned, potentially
cutting speeds drastically even if ashift is 9.
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