Date: Sat, 07 Apr 2001 19:48:11 -0600 From: Warner Losh <imp@harmony.village.org> To: Andrew Hesford <ajh3@chmod.ath.cx> Cc: Jon Molin <jon.molin@resfeber.se>, freebsd-hackers@FreeBSD.ORG Subject: Re: Adding a new drive Message-ID: <200104080149.f381nQq65746@harmony.village.org> In-Reply-To: Your message of "Sat, 07 Apr 2001 20:35:18 CDT." <20010407203518.A59413@cec.wustl.edu> References: <20010407203518.A59413@cec.wustl.edu> <20010406110817.B29989@cec.wustl.edu> <3ACD6E95.9AF73435@resfeber.se> <20010406030353.A28772@cec.wustl.edu> <3ACD7B94.300B2D49@resfeber.se> <20010406110817.B29989@cec.wustl.edu> <200104080127.f381Rjq65570@harmony.village.org>
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In message <20010407203518.A59413@cec.wustl.edu> Andrew Hesford writes: : On Sat, Apr 07, 2001 at 07:26:30PM -0600, Warner Losh wrote: : > In message <20010406110817.B29989@cec.wustl.edu> Andrew Hesford writes: : > : Hrm... I'm sorry then. I have no idea why the Handbook asks you to zero : > : out the device, it consumes a lot of time and really isn't necessary. I : > : wonder if that could be the source of your problem. : > : > The handbook should say that only the first cylendar (usually 1M) : > should be zeroed. : : Why is it important to zero out the first cylinder? I can understand : wiping the first sector to destroy the MBR (although I don't see why : this matters, either), but what makes the first cylinder special? Because our bootblock insertion code can be stupid. There are many cases when you fdisk -I and then disklabel a disk where the MBR will be hozed (I think this is only the copy of the MBR in the boot1 image located in the second track of the disk). We have found that this second copy of the MBR, which is almost always bogus, confuses things. dd of /dev/zero for the first track or so cures this and allows us to lay down correct MBR and freebsd disk label. A cylinder might be overkill, but it is what we do on the CF that we make bootable. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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