> > > What if any file/directory management would need to be done on the > secondary DC file structure if doing a straight file copy. I wouldn't want > to copy the whole directory every 15 minutes for example, but rather just > reflect the changes. > > There is a challenge with just copying changes because the journal files > can and will be re-used. This is where a replicated block device would be > nice. > > rsync will do a good job of just copying changes, even when reused b/c it does a full scan of the file to determine what (blocks) have changed.
This full scan; ie: full read to determine checksums, can be expensive on large journal files so one mitigation is to increase the number of journals in the pool and decrease the journal max file size. An ideal rsync would be aware of the current journal file append pointer though some sort of journal emitter and hence know exactly what regions can have changed. That would require a modified/customised rsync and a modified journal or some sort of write hook. If rsync on small journals does not work this could be investigated further.
