From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hubert Kario Subject: Re: Interpreting Output of "btrfs fi show" Date: Sat, 28 Apr 2012 18:42:52 +0200 Message-ID: <8118972.tgkAvno4mK@bursa22> References: Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Cc: linux-btrfs@vger.kernel.org, chris.mason@oracle.com, josef@redhat.com To: Duncan <1i5t5.duncan@cox.net> Return-path: In-Reply-To: List-ID: On Thursday 26 of April 2012 20:54:47 Duncan wrote: > Helmut Hullen posted on Thu, 26 Apr 2012 13:11:00 +0200 as excerpted: > > Hallo, Bart, > >>=20 > >> Well I think there is a btrfs superblock still present from the > >> full-disk filesystem. Due to the offset of the first partition fro= m the > >> start of the disk, this superblock was not overwritten when you cr= eated > >> the filesystem inside the partition. > >=20 > > Sounds familiar ... > >=20 > > I now use to delete about the first 10 MByte of the target disk via= "dd > > if=3D/dev/zero" >=20 > But /unlike/ reiserfs, which was only affected with the well warned a= s > don't-use-unless-you-have-to fsck --rebuild-tree option, it seems tha= t > due to btrfs scan, etc, btrfs has its similar problem in more routine > operation. I'd say that this kind of problem is basically impossible in btrfs beca= use=20 of FS UUID written all over the tree. What we see here, is a superblock that is written in *very* specific pl= ace=20 on the partition, that just is aligned in place that makes the whole di= sk=20 look like btrfs. I don't think it's actually possible for btrfs to put a file with btrfs= =20 filesystem image in place where it could seem like the basic block devi= ce=20 has btrfs /too/. It depends on whatever the metadata block is allocated= =20 before data block on disk. It /may/ be possible in mixed data-metadata=20 allocation mode. Chris or Josef, can you confirm? Still, a "zero-superblock" option would be useful for the btrfs tool. I= 'll=20 see what I can do about this. Regards, --=20 Hubert Kario QBS - Quality Business Software 02-656 Warszawa, ul. Ksawer=F3w 30/85 tel. +48 (22) 646-61-51, 646-74-24 www.qbs.com.pl -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html