Date: Thu, 18 Feb 2010 15:17:39 +1100 From: Antony Mawer <lists@mawer.org> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-stable@freebsd.org Subject: Re: netboot issues, 8.0, mfsroot mount failure Message-ID: <ea2d4a5b1002172017u2a7f71deq4d0fecd625e33f19@mail.gmail.com> In-Reply-To: <20100217192253.GA31689@icarus.home.lan> References: <alpine.OSX.2.00.1002162009030.840@hotlap.local> <20100217021136.GA10628@icarus.home.lan> <alpine.OSX.2.00.1002162337120.78881@charles-sprickmans-imac.local> <20100217192253.GA31689@icarus.home.lan>
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On Thu, Feb 18, 2010 at 6:22 AM, Jeremy Chadwick
<freebsd@jdc.parodius.com> wrote:
> On Tue, Feb 16, 2010 at 11:43:30PM -0500, Charles Sprickman wrote:
>> >Footnote: This is why I tell folks to zero out the first 8192 bytes of
>> >any disk they've previously installed FreeBSD on (even if the disk has
>> >no filesystems/slices on it). The way FreeBSD determines the size of
>> >the disk differs in RELENG_8; I believe GEOM "figures it out" on its own
>> >now, while previous releases relied on the "c" slice. The method I've
>> >recommended: do dd if=/dev/zero of=/dev/adX bs=512 count=16.
>>
>> Is it also advisable to blot out any old glabel stuff at the end of
>> the disk? What's the math to get that? Get a sector count for the
>> whole disk, set "bs" to 512 and "skip" to (sector count - 1)?
>
> I don't think the glabel data (which goes at the end of the disk) is
> relevant to the above problem I described. You can erase it if you
> want, but I doubt it's responsible for warnings like "Disk geometry does
> not match label!" or situations where a user is re-using a disk (that
> had its slices created on RELENG_7) on RELENG_8 and experiences
> problems. An alternative to the dd method might be to try "gpart
> destroy"; I haven't tried to see if relieves the problem.
>
> As far as how to erase the glabel metadata -- "glabel clear" is supposed
> to do this for you. What I don't know is whether or not addition of a
> glabel decreases what GEOM thinks the total size of the disk is, so I
> can't say for certain doing some math + zeroing the last sector of the
> disk would actually work.
I have recently been using the following snippet in an install script
to zero out any existing gmirror/etc metadata before the install
proceeds (and potentially reconfigures a new gmirror etc):
# Specify the disk device to clear
diskdev="da0"
# Clear metadata from the last sector on the drive
echo "Clearing any GEOM metadata on drive..."
diskinfo=`diskinfo /dev/$diskdev`
sector_size=`echo $diskinfo | cut -f2 -d\ `
size_in_sectors=`echo $diskinfo | cut -f4 -d\ `
geom_offset=$(($size_in_sectors-1))
dd if=/dev/zero of=/dev/$diskdev bs=$sector_size
oseek=$geom_offset count=1 2> /dev/null
In preliminary testing it seems to do the job...
-- Antony
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