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Date: Sat, 25 Jun 2016 07:29:54 -0600 (MDT)
From: Warren Block <wblock@wonkity.com>
To: Manish Jain <bourne.identity@hotmail.com>
cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org>,
 "freebsd@edvax.de" <freebsd@edvax.de>
Subject: Re: The other problem : AHCI unbootable
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On Sat, 25 Jun 2016, Manish Jain wrote:

> While installing FreeBSD 10.3 amd64, I tried switching from IDE to AHCI
> in my BIOS's boot configuration. But when I do this, the installer
> installs the OS on the hard disk, and then the system is unbootable -
> the BIOS screen hangs with the message : boot record missing.
>
> Can anyone please tell me what might be the problem ?

I have seen some systems do that not because of AHCI but because they 
have mistake preconceptions about GPT.

Setting (or clearing) the active attribute can fix this, at least for 
FreeBSD:

gpart set -a active ada0