From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: About physically swapping backing and cache device Date: Tue, 7 Jan 2014 13:35:58 -0800 Message-ID: <20140107213558.GK9037@kmo> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pb0-f42.google.com ([209.85.160.42]:52217 "EHLO mail-pb0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752691AbaAGVgC (ORCPT ); Tue, 7 Jan 2014 16:36:02 -0500 Received: by mail-pb0-f42.google.com with SMTP id uo5so671407pbc.29 for ; Tue, 07 Jan 2014 13:36:01 -0800 (PST) Content-Disposition: inline In-Reply-To: Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Josep Lladonosa Cc: "linux-bcache@vger.kernel.org" On Tue, Jan 07, 2014 at 09:52:50AM +0100, Josep Lladonosa wrote: > Hello, > > > I have been using bcache for some months. Now I am with 3.12.6 kernel > (stable! :) > Thanks and congratulations for the good work. > > I have in the laptop this configuration: > > /dev/sda7 as backing device (hard drive partition) > /dev/sdb as cache device (SSD) > > 1) I would like to physically swap sda and sdb (a matter of different > bus speeds) in order to improve ata speed for SSD. The fact is that in > a case of this, would I have to "reregister" anything in bcache, or it > will run referenced to UUIDs and so? Everything's referenced with UUIDs, so it'll all just work. > 2) I think I would have to install GRUB into /dev/sdb (it has no > partitions defined). Would it be safe installing GRUB in a cache > device? Future configuration would be /dev/sda for the cache (SSD) and > /dev/sdb for the backing device (hard drive). Bcache doesn't touch the first 4k of the device, so if it's just grub's MBR (512 bytes) that should be fine. I would verify that grub isn't touching more than the first 4k of the device though.