From mboxrd@z Thu Jan 1 00:00:00 1970 From: "A. James Lewis" Subject: layering question. Date: Tue, 04 Aug 2015 17:20:15 +0100 Message-ID: <55C0E63F.2030007@fsck.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from dozer.fsck.co.uk ([77.246.163.77]:45478 "EHLO dozer.fsck.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751837AbbHDQ3j (ORCPT ); Tue, 4 Aug 2015 12:29:39 -0400 Received: from dozer.fsck.co.uk (localhost.localdomain [127.0.0.1]) by dozer.fsck.co.uk (Postfix) with ESMTP id 31D53610014 for ; Tue, 4 Aug 2015 17:33:19 +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 03BEB610001 for ; Tue, 4 Aug 2015 17:33:18 +0100 (BST) Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org Hi all... 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 was planning to use 2 SSD's... combined with 4 large spinning drives to create a large filesystem with BTRFS... my questions are as follows. 1. Is there a way to use 2 SSD's directly, or would it be OK to use MD to stripe them?... then used the MD array as the cache device? 2. I would be using BTRFS, so would it be better to create 4 separate bcache devices each attached to the single cache device, and then use BTRFS to raid 4 bcache devices... obviously this would be more flexible, or would I need to make an MD raid of the 4 devices, and then use that to create a single bcache device and build a BTRFS filesystem on top of that. Hope that's clear, any clarification would be appreciated... Also, there's talk about a pending on-disk cache format change some time around 3.19, but no details... is this over with, or still pending? James