From mboxrd@z Thu Jan 1 00:00:00 1970 From: "A. James Lewis" Subject: Re: layering question. Date: Thu, 06 Aug 2015 01:54:12 +0100 Message-ID: <55C2B034.2090404@fsck.co.uk> References: <55C0E63F.2030007@fsck.co.uk> <20150805090446.Horde.VMReCuJzW3PwyI8Gh_BZ_yJ@www3.nde.ag> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from dozer.fsck.co.uk ([77.246.163.77]:52023 "EHLO dozer.fsck.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753072AbbHFAyP (ORCPT ); Wed, 5 Aug 2015 20:54:15 -0400 Received: from dozer.fsck.co.uk (localhost.localdomain [127.0.0.1]) by dozer.fsck.co.uk (Postfix) with ESMTP id 01D1269004C for ; Thu, 6 Aug 2015 02:09:20 +0100 (BST) Received: from [192.168.0.20] (80-46-130-192.static.dsl.as9105.com [80.46.130.192]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by dozer.fsck.co.uk (Postfix) with ESMTPSA id CD71169003F for ; Thu, 6 Aug 2015 02:09:19 +0100 (BST) In-Reply-To: Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org The problem is tho... with a very large backing store, I'm not really happy with a single point of failure in the cache... is there another way to mirror the cache device? Does anyone make an M.2 raid controller... being PCIe, I don't know it that could even be possible. James On 06/08/15 00:10, Kai Krakow wrote: > 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. >