From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Bacik Subject: Re: About btrfs chunk tree backups Date: Tue, 8 Mar 2011 10:09:37 -0500 Message-ID: <20110308150936.GA2527@localhost.localdomain> References: <4D6F58CC.9030003@cn.fujitsu.com> <20110303123724.GA4558@dhcp231-156.rdu.redhat.com> <4D75AD0D.6070501@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Josef Bacik , Chris Mason , Linux Btrfs To: Miao Xie Return-path: In-Reply-To: <4D75AD0D.6070501@cn.fujitsu.com> List-ID: On Tue, Mar 08, 2011 at 12:14:05PM +0800, Miao Xie wrote: > On Thu, 3 Mar 2011 07:37:25 -0500, Josef Bacik wrote: > > On Thu, Mar 03, 2011 at 05:01:00PM +0800, Miao Xie wrote: > >> Hi, Chris and Josef > >> > >> Recently, I am interested in chunk tree backups, which is described in > >> Project ideas web. But I found it is hard to be implemented. > >> > >> The description said "make the mappings discoverable via a block device > >> scan so that we can recover from corrupted chunk trees", I think it is > >> hard to find the boundary of each stripe, which is the constituent of > >> the chunks, via a block device scan according to the current on-disk data > >> structures. And besides that, even though we find the stripes of each > >> chunks, we still don't know the order of the stripes in one chunk. So > >> I think chunk tree backups is hard to be implemented. > >> > >> Maybe I made some mistakes in understanding this project idea? > >> > > > > We talked about this some earlier this week. This will require a format change, > > basically we need to put down some metadata at the start of every chunk so that > > we can scan the disk and find the chunks. This could probably be done in a > > backwards compatible way, we just need to make sure the space for the block > > thats used is taken up in the extent tree so old kernels don't write over the > > block. Thanks, > > Hi, Josef > > Is anyone implementing it now? Maybe we can help him to do some work. > Not that I know of. Thanks, Josef