On Thu, Feb 02, 2012 at 08:01:22PM +0100, Piergiorgio Sartor wrote: > Hi Adam, > > On Wed, Feb 01, 2012 at 03:11:54PM -0800, Adam Berkan wrote: > > When we make-bcache on a drive we need to replace the filesytem > > superblock with a bcache superblock so the kernel knows to load the > > drive through bcache, but this destroys the filesystem. We've talked > > well, I guess it will destroy the md superblock 1.1 too, > how about LVM metadata? > > I think the mismatch is with /dev/bcacheX device. > > The first implementation, as far as I remember, was simply > telling the caching device (using UUID) which was the > backing device, i.e. it was registering the backing to > the caching. > Then, still if I got it right, the bcache was caching the > backing device directly, without any need of a third > device (/dev/bcacheX). > > I understand that the actual implementation is easier and, > maybe, simpler, since a completely new device is added, > which will have the new caching "features", while the > old one (backing device) is just a further layer. > This is similar to LVM over md over /dev/sdX. The reason for getting rid of transparent caching didn't have anything to do with ease of implementation: the real reason is that safely doing persistent caching (and writeback!) is impossible with transparent caching. Adding back a mode that caches a device without a bcache superblock but without the cache being persistent isn't out of the question, but it wouldn't be terribly useful to us so it's not at all a priority for me. If someone else wrote the code I'd take patches, though. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
