From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kai Krakow Subject: Re: layering question. Date: Thu, 06 Aug 2015 01:10:49 +0200 Message-ID: References: <55C0E63F.2030007@fsck.co.uk> <20150805090446.Horde.VMReCuJzW3PwyI8Gh_BZ_yJ@www3.nde.ag> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit Return-path: Received: from plane.gmane.org ([80.91.229.3]:42498 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751305AbbHEXK5 (ORCPT ); Wed, 5 Aug 2015 19:10:57 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZN7pn-0002Lp-C5 for linux-bcache@vger.kernel.org; Thu, 06 Aug 2015 01:10:55 +0200 Received: from ip18864262.dynamic.kabel-deutschland.de ([24.134.66.98]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 06 Aug 2015 01:10:55 +0200 Received: from hurikhan77 by ip18864262.dynamic.kabel-deutschland.de with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 06 Aug 2015 01:10:55 +0200 Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org Jens-U. Mozdzen schrieb: > Zitat von Kai Krakow : >> A. James Lewis schrieb: >> >>> I've heard rumours that layering bcache with other block device drivers >>> might not be recommended... I wonder what the truth really is... perhaps >>> someone can advise. >> >> I think this is not just rumours. Multiple people reported problems when >> layering caching or backing devices on top of MD devices. This may be an >> implementation problem in MD which is gone in later kernel versions [...] > > being rather new to bcache, I did only browse the last few months of > mailing list history - are you saying that these problems were fixed > (or simply vanished) some point after 3.18.8? Because if so, I'd of > course try to upgrade our servers to a more recent kernel :) Latest posts imply it is still a problem. It fits with earlier reports: Caching on native device, backing on md device... Bcache breaks within the caching device (although this is not on md). There seem to still be bugs with bcache and md to properly interact. It was suspected that bcache uses a faulty discard implementation. Some reports miss details about this setting. However, my setups are working fine with discards fully enabled on SSD - but without using MD. And it has been robust to accidental or implied reboots since all time I'm using it (even with btrfs as the filesystem on bcache). So I'd probably remove MD from your plans on using bcache. BTW: My system uses vanilla gentoo kernel, 4.1.4 currently. -- Replies to list only preferred.