[dm-devel] Newbie device mapper questions

[Alasdair G Kergon]

On Mon, Jun 15, 2015 at 08:39:54PM +0200, Johannes Bauer wrote:
> Something that I would like to implement first is a device mapper target
> that takes three block devices as input: Two equally sized devices (src1
> and src2) and a separate metadata device (meta). I want to map chunks of
> the src devices to bits of a bitmap in the meta device. If the bit is
> set in the meta device decides whether src1 and src2 is returned.
 
The dm-switch target already provides this functionality under the control of
userspace.  Userspace can maintain/monitor your metadata device and send
messages to the kernel whenever there are changes.

Alasdair