From owner-freebsd-fs@FreeBSD.ORG  Wed Nov 19 11:09:36 2014
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id D3C098F3
 for <freebsd-fs@FreeBSD.org>; Wed, 19 Nov 2014 11:09:36 +0000 (UTC)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
 by mx1.freebsd.org (Postfix) with ESMTP id 2D703653
 for <freebsd-fs@FreeBSD.org>; Wed, 19 Nov 2014 11:09:35 +0000 (UTC)
Received: from porto.starpoint.kiev.ua (porto-e.starpoint.kiev.ua
 [212.40.38.100])
 by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id NAA21858;
 Wed, 19 Nov 2014 13:11:19 +0200 (EET) (envelope-from avg@FreeBSD.org)
Received: from localhost ([127.0.0.1])
 by porto.starpoint.kiev.ua with esmtp (Exim 4.34 (FreeBSD))
 id 1Xr38Y-0004dO-Hr; Wed, 19 Nov 2014 13:09:26 +0200
Message-ID: <546C7A29.9020103@FreeBSD.org>
Date: Wed, 19 Nov 2014 13:08:25 +0200
From: Andriy Gapon <avg@FreeBSD.org>
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64;
 rv:31.0) Gecko/20100101 Thunderbird/31.2.0
MIME-Version: 1.0
To: Steven Hartland <killing@multiplay.co.uk>, freebsd-fs@FreeBSD.org
Subject: Re: No more free space after upgrading to 10.1 and zpool upgrade
References: <CA+q+Tcqo2CL+00-4RTD1=WStOSYtawwsZbC1tpZ1G9CbiBp_Dw@mail.gmail.com>
 <20141116080128.GA20042@exhan.dylanleigh.net>
 <CA+q+TcoC4gTPqGc_V3xv+cWxJuB2r8YioH_NLfaj=5xwsaXW0w@mail.gmail.com>
 <20141118054443.GA40514@core.summit> <546B8203.5040607@platinum.linux.pl>
 <546B9754.4060906@delphij.net> <20141119013611.GA52102@core.summit>
 <546C01C5.7080605@delphij.net> <546C18F4.1090209@multiplay.co.uk>
In-Reply-To: <546C18F4.1090209@multiplay.co.uk>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 8bit
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs/>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 19 Nov 2014 11:09:36 -0000

On 19/11/2014 06:13, Steven Hartland wrote:
> The new space map code should help with that and a fixed 3.125% is a large
> portion of a decent sized pool.
> 
> On our event cache box for example thats 256GB which feels like silly amount to
> reserve.
> 
> Does anyone have any stats which backup the need for this amount of free space
> on large pool arrays, specifically with spacemaps enabled?

There was a presentation about the spacemap code at the OpenZFS Devsummit.
One point is that going above 95% will kill performance (actually sooner).  This
is applicable to all spacemap algorithms currently available.

There is a pretty graph at page 13 here
http://open-zfs.org/w/images/3/31/Performance-George_Wilson.pdf
-- 
Andriy Gapon