Re: Btrfs disk layout question

[Chris Murphy <lists@colorremedies.com>]

On Sat, Apr 15, 2017 at 12:14 AM, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
> 12.04.2017 20:21, Chris Murphy пишет:
>> btrfs-map-logical is the tool that will convert logical to physical
>> and also give what device it's on; but the device notation is copy 1
>> and copy 2, so you have to infer what device that is, it's not
>> explicit.
>>
>
> Actually I just checked with btrfsprogs 4.5.3 on RAID5 and it does print
> OS device name for each data chunk. It does not show checksum chunk for
> RAID56 though.

There is no checksum chunk. The data csums are in their own tree, and
only data is csum'd. The parity strip is contained within a raid56
chunk but is itself not csum'd.

Another thing that I just thought of might be useful is btrfs-debugfs
which is a python script in btrfs-progs, but typically not packaged.
The -f option pointed at a file will show extents with Btrfs logical
bytenr. So that'd be a way to get all the extents, their addresses and
lengths, to then dump into btrfs-map-logical.

For what it's worth, btrfs-map-logical's physical address it reports
is not device LBA. It's a byte offset on the selected device. So if
the device is a partition, the value is the number of bytes from the
start of that partition.



-- 
Chris Murphy