From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from frost.carfax.org.uk ([85.119.82.111]:39104 "EHLO frost.carfax.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753141AbbI2MVm (ORCPT ); Tue, 29 Sep 2015 08:21:42 -0400 Date: Tue, 29 Sep 2015 12:21:39 +0000 From: Hugo Mills To: Austin S Hemmelgarn Cc: dsterba@suse.cz, =?iso-8859-1?Q?Gabr=EDel_Arth=FAr_P=E9tursson?= , linux-btrfs@vger.kernel.org Subject: Re: Add stripes filter Message-ID: <20150929122139.GF25907@carfax.org.uk> References: <1443463025.16163.6.camel@system.is> <20150929120029.GX11442@twin.jikos.cz> <560A7FAB.1040607@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="SxgehGEc6vB0cZwN" In-Reply-To: <560A7FAB.1040607@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: --SxgehGEc6vB0cZwN Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Sep 29, 2015 at 08:10:19AM -0400, Austin S Hemmelgarn wrote: > On 2015-09-29 08:00, David Sterba wrote: > >On Mon, Sep 28, 2015 at 05:57:05PM +0000, Gabr=EDel Arth=FAr P=E9tursson= wrote: > >>The attached patches to linux and btrfs-progs add support for filtering > >>based on the number of strips in a block when balancing. > > > >What usecase do you want to address? As I understand it, this would help > >the raid56 rebalancing to process only blockgroups that are not spread > >accross enough devices. Exactly. Last week, I was trying to help Gabr=EDel on IRC with a close-to-full filesystem balance it to add some new devices in a parity RAID configuration. He'd added the devices and balanced, but the usage was unequal across the devices. The only way I could think of dealing with it with the current tools was either to do a full balance repeatedly until it worked itself out, or to delve into the metadata with btrfs-debug-tree, and balance selected block groups individually. I whinged that we needed a filter to pick just the block groups that weren't "as full as possible", and Gabr=EDel picked up the idea and ran with it. > This could also be helpful when reshaping a raid10 or raid0 setup. Yes, although ultimately less important in most cases, I think, because you don't lose space by reducing the number of devices in a block group for those. There are some corner cases where you could end up losing space by having one (for RAID-0) or up to three (for RAID-10) devices with more space left than the rest. Hugo. --=20 Hugo Mills | Dullest spy film ever: The Eastbourne Ultimatum hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 | The Thick of= It --SxgehGEc6vB0cZwN Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJWCoJTAAoJEFheFHXiqx3krEAP/2Uv0jFUZlh+nbotVLZ9jgrp suuB01vUnHySqKSs0Yc6viYsGUBV3sadgGU4px+Y2rbZFM00rzYyI7qbHOEUSegN g8ZXKya+xu+AYLQojBiSYj/eNXmyMYPFbi8koz4+/EYh2iFI6JuKgfzGGSzYSYYm rzpbivviB3OBxQ3fCj5mYEJ/I/phz6HVcFmvVUikRWACO4Iuq9GxYTS5HgmwGK7h 6nUxdMPA5DtEPv3gEgzffRpk+STdSBtyv3ADxJMS9gOif8flimIihK8ITinZM+zP B/yNGr2EFhB8CJGxSpQXvpZBOtSY9Vory9RtCosDLp6SPHeQQzSZmUR2R9K9uL5l svSHBcUGk7TgStBHzJuauZk3xqAPRFWR6H/NZrfwwk/LUyfmRkt7qIfQZtDtMwBN ibi328GOYaUk41AnUae63SDKbXzgorvEJ/YJxILpcG0FZEBvKQRcwag08O82Bav1 l2/LzNZLrww7Ws+dnXgY4axKZdPh1QWpfDnUcpCytnHNj+xOxHAGkwKwHY0zjlQs 0Gqb9gmKwSmx2FL4DWX4VI1ZBYWMuJGj9+0tOZY+qiD4icWyuUCKpeqeRdbTm+Xf xPa9rnZ2xYZymQ4eNXXkmHVZs+sr5P5T+iSP2pgKxkJ/p7ojLR+na7rE3QXXGTfX 8nw30VVcqg8USg5Bf+lI =5bio -----END PGP SIGNATURE----- --SxgehGEc6vB0cZwN--