From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f66.google.com ([74.125.82.66]:33422 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750862AbdISPac (ORCPT ); Tue, 19 Sep 2017 11:30:32 -0400 Received: by mail-wm0-f66.google.com with SMTP id m127so4246592wmm.0 for ; Tue, 19 Sep 2017 08:30:32 -0700 (PDT) Received: from [10.3.28.18] ([155.210.222.97]) by smtp.gmail.com with ESMTPSA id u186sm1679963wmd.19.2017.09.19.08.30.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 19 Sep 2017 08:30:30 -0700 (PDT) To: Btrfs BTRFS From: Pat Sailor Subject: SSD caching an existing btrfs raid1 Message-ID: <4ed24e33-09e1-c03a-912c-9d1b2bbdc835@gmail.com> Date: Tue, 19 Sep 2017 17:30:30 +0200 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: Hello, I have a half-filled raid1 on top of six spinning devices. Now I have come into a spare SSD I'd like to use for caching, if possible without having to rebuild or, failing that, without having to renounce to btrfs and flexible reshaping. I've been reading about the several options out there; I thought that EnhanceIO would be the simplest bet but unfortunately I couldn't get it to build with my recent kernel (last commits are from years ago). Failing that, I read that lvmcache could be the way to go. However, I can't think of a way of setting it up in which I retain the ability to add/remove/replace drives as I can do now with pure btrfs; if I opted to drop btrfs to go to ext4 I still would have to offline the filesystem for downsizes. Not a frequent occurrence I hope, but now I'm used to keep working while I reshape things in btrfs, and it's better if I can avoid large downtimes. Is what I want doable at all? Thanks in advance for any suggestions/experiences to proceed.