Date: Fri, 30 Dec 2016 12:02:44 -0700 From: Ian Lepore <ian@freebsd.org> To: "Andrey V. Elsukov" <ae@FreeBSD.org>, Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: freebsd-hackers@freebsd.org Subject: Re: How to safely remove rest of GTP? Message-ID: <1483124564.16152.85.camel@freebsd.org> In-Reply-To: <071295b5-f7d8-d09b-13f9-416524a1f654@FreeBSD.org> References: <20161230124407.GN37118@zxy.spb.ru> <d79b8568-72e8-415e-4923-14e3c730267e@FreeBSD.org> <20161230164652.GO37118@zxy.spb.ru> <22d5dece-f14b-3bef-b3dd-8bb6226e0d28@FreeBSD.org> <1483119430.16152.83.camel@freebsd.org> <071295b5-f7d8-d09b-13f9-416524a1f654@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, 2016-12-30 at 20:48 +0300, Andrey V. Elsukov wrote: > On 30.12.2016 20:37, Ian Lepore wrote: > > > > > > > > In case when you have not valid primary header, `gpart destroy` > > > will > > > not > > > touch first two sectors. In you case you can wipe only last > > > sector, > > > like > > > Ian suggested, but use 'gpart destroy -F da6' instead of dd. > > > > > If you gpart destroy -F da6 won't that also clear the valid MBR at > > the > > start of the disk? I think Slawa needs to preserve that. > As I said, it will not touch first two sectors, where PMBR and > primary > GPT headers are. > > > > > I think it would be really useful if gpart recover could help with > > this > > somehow. There is a valid mbr, and a partially-valid gpt (only the > > backup is valid). So gpart recover should provide a way to recover > > the > > gpt by refreshing the primary gpt and the pbmr, > `gpart recover` will restore GPT using information from backup > header > and table and construct new PMBR. After that you need to write > bootcode > if needed. > > > > > or recover the mbr by > > wiping the backup gpt. > This is what the patch does. You need to use `gpart destroy -F` to > CORRUPTED GPT, this command will wipe last sector where GPT backup > header is located. Since GPT is in CORRUPT state, the primary header > will not be overwrited by this command. > > When both primary and backup headers and tables are valid, `gpart > destroy` overwites PMBR, primary and backup headers. > > > > > I'm not sure what the syntax would be to > > specify that, though. > > > > This didn't used to be a problem until the changes that made the > > backup > > gpt get used automatically without any sysadmin intervention. > For some users the problem was that they could not find their GPT, > that > declares its reliability. > Do you seriously believe that people are going to just do a gpart destroy -F on a device with a valid MBR as a method of preserving that mbr? If that's the kind of thinking behind the gpart interface, I guess that helps explain why it's so nearly impossible to understand and use already. -- Ian
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?1483124564.16152.85.camel>