On Sat, May 04, 2013 at 11:17:36AM +1000, Dmitry Smirnov wrote: > On Sat, 4 May 2013 04:45:00 Ben Hutchings wrote: > > According to <https://lwn.net/Articles/548348/>, bcache is going into > > Linux 3.10 (though it now looks like it has missed that). With > > dm-cache and bcache in the kernel, would there still be a need for > > this third option? > > Good question. :) > > I didn't have a chance to examine dm-cache yet but I tried others. > > To me bcache is the most worthless of all because it requires > specially prepared (formatted) data partition. This makes it difficult > (if possible) to attach cache to existing partition with data as one > would need 200% capacity and to perform long data-moving in order to > activate/deactivate caching. I don't know if this fundamental > show-stopper changed since I tried bcache. Besides bcache also > requires modified kernel which is limiting its "field of endeavour" > even further.
But it won't require a modified kernel in future. That's my point. > We packaged flashcache when there were no other feasible alternatives. > To use flashcache it is necessary to create a virtual device-mapper > device that combines data and cache devices. Assuming that data > partition already have data it is only needed to mount it through > associated flashcache device. > > The brilliance of EnhanceIO is that it doesn't need intermediate > device at all and can be attached to any block device on-the-fly even > when device is already mounted. [...] Bcache can apparently do that as well, but as you noted the backing device must have been prepared with a bcache superblock. Apparently the reasoning for this is to prevent accidental access that bypasses the cache. It seems like this could be relaxed if the cache is configured for write-through behaviour, though. Ben. -- Ben Hutchings We get into the habit of living before acquiring the habit of thinking. - Albert Camus -- To UNSUBSCRIBE, email to debian-wnpp-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20130504015016.go2...@decadent.org.uk