How to make a block-level incremental backup using LVM?

[Gordon Messmer]

On 12/14/2012 08:04 AM, Fernando Lozano wrote:
> I suppose they use something like inotify (or their own virtual file
> system driver over a real file system, like NFS or a loop fs) to learn
> about changed blocks, but they find to which file each block belongs to
> and salve this info in their backup catalog. If the changed block is
> filesystem (or md device, or lvm) metadata, they have to understand this
> and eithert log the change apropriately or ignore it as it's not file data.
>
> I can imagine something like this working and even how to program. And
> I'm a little scared about some backup tool being monitoring my file
> accesses all the time. ;-)

Conceptually, that is too complicated.  All that the software has to do 
is track block changes and replicate them to a block device or virtual 
block device at the backup server.  The software doesn't have to care 
whether it's data or metadata, the destination server just needs to be 
able to mount the block device / virtual block device.  Windows systems 
probably implement that with VHD.  Free Software systems can do that 
with a variety of filesystems, though typically replication would need 
to stop while the block device is mounted.