From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f52.google.com ([209.85.214.52]:35544 "EHLO mail-it0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755843AbcILNBL (ORCPT ); Mon, 12 Sep 2016 09:01:11 -0400 Received: by mail-it0-f52.google.com with SMTP id r192so7254648ita.0 for ; Mon, 12 Sep 2016 06:01:11 -0700 (PDT) Subject: Re: Small fs To: Imran Geriskovan , Chris Murphy References: Cc: Btrfs BTRFS From: "Austin S. Hemmelgarn" Message-ID: <9d4c732d-bd0b-bd1d-2351-317ae3a38ebb@gmail.com> Date: Mon, 12 Sep 2016 09:01:07 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2016-09-12 08:54, Imran Geriskovan wrote: > On 9/11/16, Chris Murphy wrote: >> Something else that's screwy in that bug that I just realized, why is >> it not defaulting to mixed-block groups on a 100MiB fallocated file? I >> thought mixed-bg was the default below a certain size like 2GiB or >> whatever? > >>> With an ordinary partition on a single disk, >>> fs created with just "mkfs.btrfs /dev/sdxx": >>> - 128MB works fine. >>> - 127MB works but as if it is 64MB. >>> Can we say size should be in multiples of 64MB? > >> Why should it be in multiples? I think what you're describing is part >> of the bug above that just needs to be fixed. Btrfs itself internally >> uses bytes, so multiples of 64MiB is OK but I wouldn't use the word >> "should" with it. > > I'm not suggesting anything. I'm just describing the behaviour > we've seen. If it is (or will be) something different its all ok for me. > > But, what is that "formal behaviour" at the low end? > That is the discussion.. Formally, with mixed-bg and otherwise default options, you should be able to get to about 48-49% of the total size of the FS worth of data stored. In practice, I see such filesystems start having issues at about 45% of the total size. Note that this is not the percentages reported by regular df (which should say about 90% full in this case), b ut a comparison based on du -sh and the size of the partition.