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.
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