From owner-freebsd-hackers@FreeBSD.ORG Tue Jan 22 18:19:00 2013 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 7E3C9FA7 for ; Tue, 22 Jan 2013 18:19:00 +0000 (UTC) (envelope-from matthew.ahrens@delphix.com) Received: from mail-lb0-f173.google.com (mail-lb0-f173.google.com [209.85.217.173]) by mx1.freebsd.org (Postfix) with ESMTP id 07B33ABE for ; Tue, 22 Jan 2013 18:18:59 +0000 (UTC) Received: by mail-lb0-f173.google.com with SMTP id gf7so4659099lbb.18 for ; Tue, 22 Jan 2013 10:18:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=delphix.com; s=google; h=mime-version:x-received:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; bh=qIMylib9uTp3ioe2QABsre9UeXFqZcBxYifHZU4Sgqk=; b=GQGa23gi7gjOeKmCQC/jTv4yvJvdl8ZCqTyFW7y+1xaaDHMHwcXznPz8BWc6TCC8a8 cjzMxA2yYe9blMXNKxmwlWF6/1iPEF+01TozCVu3G77ztY9N5FHNX2dGA8XZRE2iW0E9 cgWMAovrbVXWvhR5CepPwxTXVU/C/qqc0coGg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=mime-version:x-received:in-reply-to:references:date:message-id :subject:from:to:cc:content-type:x-gm-message-state; bh=qIMylib9uTp3ioe2QABsre9UeXFqZcBxYifHZU4Sgqk=; b=B2LU/JohtZOOGVp5FiFiYpigJYmhVWUU7YFggZrJ33iqvtzhYTXM/pP/jkxfFMz68c LoxoOfUgYRkh0Pv2nOs6khUgAbFXnJMQAYFtqldGscMHBuTj6YYSZi9u1p7+B2nqJjf8 niJQKO9OU1FkyVOlB5lZFTwwyAiSostXvgONCzp3o4ZGN4FLC8sLnUJwxevGl3W/99tE hniUgAssARPZbr/nTMHsw54em/+LgWgXQw0atOhZYf4uX1ZAoJuJrEPMRn9lMNF5gUd0 /11209QGJmouMFnKFRpzcqhrDurwod6lo8vovRtDWBeJIPWcAcpDxB+6Dd3H0TCC5rzt JOPA== MIME-Version: 1.0 X-Received: by 10.112.88.105 with SMTP id bf9mr9704257lbb.43.1358878732612; Tue, 22 Jan 2013 10:18:52 -0800 (PST) Received: by 10.114.63.100 with HTTP; Tue, 22 Jan 2013 10:18:52 -0800 (PST) In-Reply-To: <20130122073641.GH30633@server.rulingia.com> References: <20130122073641.GH30633@server.rulingia.com> Date: Tue, 22 Jan 2013 10:18:52 -0800 Message-ID: Subject: Re: ZFS regimen: scrub, scrub, scrub and scrub again. From: Matthew Ahrens To: Peter Jeremy X-Gm-Message-State: ALoCoQlOUch9HKcnvBP7fjAontjXsBpFkOFxjFGE4T44f/sBOrXXYkfP6swk32rAs3vlHO7ui7oG X-Mailman-Approved-At: Tue, 22 Jan 2013 18:31:27 +0000 Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.14 Cc: freebsd-fs , Wojciech Puchar , FreeBSD Hackers X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 22 Jan 2013 18:19:00 -0000 On Mon, Jan 21, 2013 at 11:36 PM, Peter Jeremy wrote: > On 2013-Jan-21 12:12:45 +0100, Wojciech Puchar < wojtek@wojtek.tensor.gdynia.pl> wrote: >>While RAID-Z is already a king of bad performance, > > I don't believe RAID-Z is any worse than RAID5. Do you have any actual > measurements to back up your claim? Leaving aside anecdotal evidence (or actual measurements), RAID-Z is fundamentally slower than RAID4/5 *for random reads*. This is because RAID-Z spreads each block out over all disks, whereas RAID5 (as it is typically configured) puts each block on only one disk. So to read a block from RAID-Z, all data disks must be involved, vs. for RAID5 only one disk needs to have its head moved. For other workloads (especially streaming reads/writes), there is no fundamental difference, though of course implementation quality may vary. >> Even better - use UFS. To each their own. As a ZFS developer, it should come as no surprise that in my opinion and experience, the benefits of ZFS almost always outweigh this downside. --matt