Re: About btrfs chunk tree backups

[Miao Xie <miaox@cn.fujitsu.com>]

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.

Thanks
Miao

> 
> Josef 
>