From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6473FC43331 for ; Tue, 12 Nov 2019 14:28:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 418AE222C5 for ; Tue, 12 Nov 2019 14:28:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727078AbfKLO2Y (ORCPT ); Tue, 12 Nov 2019 09:28:24 -0500 Received: from briare1.fullpliant.org ([78.227.24.35]:57492 "HELO briare1.fullpliant.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726008AbfKLO2Y (ORCPT ); Tue, 12 Nov 2019 09:28:24 -0500 X-Greylist: delayed 900 seconds by postgrey-1.27 at vger.kernel.org; Tue, 12 Nov 2019 09:28:24 EST From: Hubert Tonneau To: linux-btrfs@vger.kernel.org Subject: Avoiding BRTFS RAID5 write hole Date: Tue, 12 Nov 2019 15:13:26 GMT Message-ID: <0JG8IAF11@briare1.fullpliant.org> X-Mailer: Pliant 114 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi, In order to close the RAID5 write hole, I prepose the add a mount option that would change RAID5 (and RAID6) behaviour : . When overwriting a RAID5 stripe, first convert it to RAID1 (convert it to RAID1C3 if it was RAID6) . Have a background process that converts RAID1 stripes to RAID5 (RAID1C3 to RAID6) Expected advantages are : . the low level features set basically remains the same . the filesystem format remains the same . old kernels and btrs-progs would not be disturbed The end result would be a mixed filesystem where active parts are RAID1 and archives one are RAID5. Regards, Hubert Tonneau