Date: Wed, 17 Feb 2010 11:22:53 -0800 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: freebsd-stable@freebsd.org Subject: Re: netboot issues, 8.0, mfsroot mount failure Message-ID: <20100217192253.GA31689@icarus.home.lan> In-Reply-To: <alpine.OSX.2.00.1002162337120.78881@charles-sprickmans-imac.local> References: <alpine.OSX.2.00.1002162009030.840@hotlap.local> <20100217021136.GA10628@icarus.home.lan> <alpine.OSX.2.00.1002162337120.78881@charles-sprickmans-imac.local>
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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. -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |
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