Date: Fri, 28 Sep 2012 16:53:10 -0700 From: Xin Li <delphij@delphij.net> To: Warren Block <wblock@wonkity.com> Cc: freebsd-geom@freebsd.org Subject: Re: Simple way to clear arbitrary drive metadata? Message-ID: <50663866.9070001@delphij.net> In-Reply-To: <alpine.BSF.2.00.1209281607310.20482@wonkity.com> References: <alpine.BSF.2.00.1209281607310.20482@wonkity.com>
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 09/28/12 15:21, Warren Block wrote: > Last night, I found that the remnants of a GPT backup table on an > MBR drive prevented it from booting. When reusing drives from old > mirrors, old mirror metadata can be a problem also. And there may > be old hardware RAID metadata at the end of the drive. > > It would be great if dd understood negative seek values. This > would get most of that old metadata: > > dd if=/dev/zero of=/dev/ada8 seek=-34 > > ...but dd does not understand negative seek values. (Been on my > list for a while to look at that.) > > Which leaves things like > > diskinfo ada8 | cut -f4 (subtract 34) dd if=/dev/zero of=/dev/ada8 > seek=(calculated value) > > That can be done in one command line with bc and backticks, but > it's not clear or elegant. gpart can clear secondary GPT tables, > but I'm pretty sure it won't wipe out that space unless it actually > is a GPT table. Likewise with glabel and gmirror, they're safe > because they only touch data they understand. > > Is there something simpler and more blunt? I think you can do: gpart destroy -F ada8 gpart create -s gpt ada8 gpart destroy -F ada8 The second 'create' will write an empty partition table to the secondary table. Cheers, - -- Xin LI <delphij@delphij.net> https://www.delphij.net/ FreeBSD - The Power to Serve! Live free or die -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBCAAGBQJQZjhmAAoJEG80Jeu8UPuzp/wIAJ9TQdwRIvfMn5zP3yMqYKIV OvVNSUaecPaav9G7CEwApl1bQnmCSYepv6FASH65CoNyr14kioS0e8BET4s/GzQD LhliFucVnd6X6POdyL5VEdJ78UYuox8h9elykJBSlwdgeWGCpoRwI9sG8+oWtl+Z zpYKgUBU+eCTsXWjIBbLGphhgXgDT+j1uEks8qxbVsUNZH054tKWEQ6iK2+bKGYa 6dp3M+Lrt6qJLcKWtFvxMVP2rzCzYmRmSFkKVUiIHgSOp2yH4uFvzRo9CY74azuL QS4/+h5iuMtnMiXKr5sWoGOi4WCTLVSnmo07ac9aP4H0jlTuVmJ/Qq/hoqOuMZg= =ae1M -----END PGP SIGNATURE-----
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