> -----Original Message----- > From: centos-bounces at centos.org > [mailto:centos-bounces at centos.org] On Behalf Of Ross Walker > Sent: Friday, August 14, 2009 10:30 > To: CentOS mailing list > Subject: Re: [CentOS] OT: Fortunate clueless dd chum - lvm recovery > > On Fri, Aug 14, 2009 at 5:00 AM, Chan Chung Hang > Christopher<christopher.chan at bradbury.edu.hk> wrote: > > > >> > >> First of all, I would dd a copy of the whole drive off to > another drive, so you can have a few goes at this. > >> > >> How do you know only those bits where lost? > >> > > > > The dd command zeros the first 64 sectors, that is, the mbr > and then > > the next 63 sectors which would the bootsector of the first > partition > > and the next 62 sectors following that. The first partition on both > > disks belong to the md device that is the basis for the physical > > volume for the system. And if it had not, it would have belonged to > > the md device for the /boot partition which is not a great loss. > > Default Redhat layout this. > > > > The box is still live and I am glad he was not clueless > enough to say > > yes to the mkefs2 command he was following from whatever > howto he had > > been looking at. It looks like the lvm survived having the first 62 > > sectors being zeroed. Apparently lvm uses the first 255 > sectors/blocks > > for lvm config data. No alarms/warnings in the logs. Certainly no > > panics otherwise I would not even be able to get in. > > > > I get to learn something new at his expense, (which is now just a > > scare) nice successor eh? :-D > > > > Absolutely zero data loss. What can I say? > > Well if he dd'd 64 sectors instead of 63 then the first > sector of the first partition is going to be zero'd too. > > Backup the data while the stale partition table is still in memory! > > A reboot will make it inaccessible. > > Try a: > > # sfdisk -d /dev/sdX >/root/sdX.save ROTFLMAO, you should make sure, before copying and pasting that /root/sdX.save does not exist. > > Look at it and see if it contains a valid partition table, if > it does then do a: > > # sfdisk --no-reread /dev/sdX </root/sdX.save > > Question now is, was the first sector of partition 1 damaged (was it > 63 or 64 sectors dd'd)? > > If so it will require a more tricky procedure to fix. > > -Ross > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- - - - Jason Pyeron PD Inc. http://www.pdinc.us - - Principal Consultant 10 West 24th Street #100 - - +1 (443) 269-1555 x333 Baltimore, Maryland 21218 - - - -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- This message is copyright PD Inc, subject to license 20080407P00.