From mboxrd@z Thu Jan 1 00:00:00 1970 From: Piergiorgio Sartor Subject: Re: Formatting of backing device Date: Thu, 2 Feb 2012 23:24:31 +0100 Message-ID: <20120202222431.GA7171@lazy.lzy> References: <20120201101041.GA2779@lazy.lzy> <20120201205456.GA7669@lazy.lzy> <20120201214443.GA8544@lazy.lzy> <20120202190122.GA2353@lazy.lzy> <20120202221101.GA26768@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20120202221101.GA26768-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Kent Overstreet Cc: Piergiorgio Sartor , Adam Berkan , linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org Hi Kent, nice to have you in this discussion! > > 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. Well, it seems to me "impossible" is a big word... I could image is more "invasive". > 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 I miss the point, the superblock can be stored in the caching device, instead of the backing and the actual device *could* stay the same. The kernel would have to discover first the caching, later the backing and then put things together. So, the cache will be persistent, or? As I wrote above, I see this more complex than adding a further layer, likely I would do the same. > 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. No time for that, unfortunately. I take the opportunity to congratulate personally to you for this project, well done! bye, -- piergiorgio