On Fri, Jun 10, 2011 at 1:11 PM, Joe Thornber <thornber@xxxxxxxxxx> wrote: > On Fri, Jun 10, 2011 at 11:01:41AM +0200, Lukas Czerner wrote: >> On Fri, 10 Jun 2011, Amir G. wrote: >> >> > CC'ing lvm-devel and fsdevel >> > >> > >> > On Wed, Jun 8, 2011 at 9:26 PM, Amir G. <amir73il@xxxxxxxxxxxxxxxxxxxxx> wrote: >> > For the sake of letting everyone understand the differences and trade >> > offs between >> > LVM and ext4 snapshots, so ext4 snapshots can get a fair trial, I need >> > to ask you >> > some questions about the implementation, which I could not figure out by myself >> > from reading the documents. > > First up let me say that I'm not intending to support writeable > _external_ origins with multisnap. This will come as a suprise to > many people, but I don't think we can resolve the dual requirements to > efficiently update many, many snapshots when a write occurs _and_ make > those snapshots quick to delete (when you're encouraging people to > take lots of snapshots performance of delete becomes a real issue). > If I understand this article correctly: http://people.redhat.com/mpatocka/papers/shared-snapshots.pdf It says that _external_ origin write updates can be efficient to readonly (or not written) snapshots. Could you not support readonly snapshots of an _external_ origin? You could even support writable snapshots, that will degrade write performance to origin temporarily. It can be useful, if one wants to "try-out" mounting a temporary writable snapshot, when the origin is not even mounted. After the "try-out", the temporary snapshot can be deleted and origin write performance would go back to normal. Is that correct? Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
