On Thu, Jan 9, 2014 at 1:02 PM, J. R. Okajima <hooanon05g@xxxxxxxxx> wrote: > > Saket Sinha: >> > For such purpose, a "block device level union" (instead of filesystem >> > level union) may be an option for you, such as "dm snapshot". >> > >> I imagine that this would make things more complicated as ideally this >> should be done in a filesystem driver. Again a "block device level >> union" would all the more have lesser chances of getting this >> filesystem driver included in the mainline kernel as kernel >> maintainers prefer the drivers to be as simple as possible. > > ?? > I am afraid that I cannot fully understand what you wrote. I am sorry for not explaining it properly. I was abrupt and hence was misunderstood. My fault!. > If you think "dm snapshot" does not exist currently, and you or someone > else are going to develop a new feature, that is wrong. You already have > "dm snapshot" feature and you can "stack" the block devices by using it. > (cf. http://aufs.sourceforge.net/aufs2/report/sq/sq.pdf which is a bit > old) NO. I know it very much exists. It forms the foundation of LVM2, software RAIDs, dm-crypt disk encryption, and offers additional features such as file system snapshots and I do not doubt either its functionality or usage. What I am referring here is the topic <storing metadata in multiple places vs "block device level union">. See DM operates on block device/sector, but a stackable filesystem operates on filesystem/file. My point is this that which is the better approach according to the kernel maintainers, so that this concept of Unioning gets universally accepted and we have a mainline kernel union filesystem. Regards, Saket Sinha -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
