From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) by finch.gentoo.org (Postfix) with ESMTP id 8467F1381F3 for ; Thu, 19 Sep 2013 13:02:01 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 9A1AEE0B31; Thu, 19 Sep 2013 13:01:48 +0000 (UTC) Received: from mail-qa0-f47.google.com (mail-qa0-f47.google.com [209.85.216.47]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id 93693E0869 for ; Thu, 19 Sep 2013 13:01:47 +0000 (UTC) Received: by mail-qa0-f47.google.com with SMTP id k4so3548064qaq.6 for ; Thu, 19 Sep 2013 06:01:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=GbmvKkicNLMdvwgdTE4ytvyU4Ro4jsPBmLr5jmMd8uA=; b=QyvE8VrVVGu9h8ARCUk88X/jyJzL4S9TmwHbUkUYrCMTpS8ZT7FG45JfQMOwm0ow+j NMfJyFD2x/HHEJfVpx04dFNn+OTr9CoGiVhrjhuW/QwYnPEl6S/yHO1ZQwhB20nneDKt EQpMc8gF7V7z1W7zuq5YrXbuMBtzq3T4uPRV8o2fKTtFsp9+oBQHLEWxDflO1dkpx/vQ H+5K/1RcXhmObGey7cytthQXE1cb+1Fqt5Yjr9b7+oA04UU96TLr0+cnsN0Pjgf96kdn YHOp/irsccZEg7q96LdA9bdTKKMSaLm+JxR8Cj5elHoyD0h3oKOYvCqLmHABBTKFeYFM ze+g== Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org MIME-Version: 1.0 X-Received: by 10.49.27.137 with SMTP id t9mr3254096qeg.70.1379595706733; Thu, 19 Sep 2013 06:01:46 -0700 (PDT) Received: by 10.140.25.83 with HTTP; Thu, 19 Sep 2013 06:01:46 -0700 (PDT) In-Reply-To: References: <523898A3.7000404@googlemail.com> <52389B55.6090600@libertytrek.org> <20130918042228.GG25579@server> <20130919074441.GB12275@TranscendTheRubicon.fritz.box> <523AD3F2.40301@libertytrek.org> Date: Thu, 19 Sep 2013 13:01:46 +0000 Message-ID: Subject: Re: [gentoo-user] Re: ZFS From: Grant To: Gentoo mailing list Content-Type: text/plain; charset=ISO-8859-1 X-Archives-Salt: d1bd1561-f7bb-43d0-9161-2ec80bbeb42c X-Archives-Hash: 3dd0a1f2021974e9d67704ae46f248a7 >>> You should definitely determine the right value for ashift on pool >>> creation >>> (it controls the alignment on the medium). It's an option that you afaik >>> can only set >>> on filesystem creation and therefore needs a restart from scratch if you >>> get it >>> wrong. >>> According to the illumos wiki it's possible to run a mixed pool (if you >>> have >>> drives requiring different alignments[1]) >>> If in doubt: ask ryao (iirc given the right information he can tell you >>> which >>> are the right options for you if you can't deduce it yourself). >>> Choosing the wrong alignment can cause severe performance loss (that's not >>> a ZFS issue but happened when 4k sector drives appeared and tools like >>> fdisk >>> weren't aware of this). >> >> Yikes... >> >> Ok, shouldn't there be a tool or tools to help with this? Ie, boot up on a >> bootable tools disk on the system with all drives connected, then let it >> 'analyze' your system, maybe ask you some questions (ie, how you will be >> configuring the drives/RAID, etc), then spit out an optimized config for >> you? >> >> It is starting to sound like you need to be a dang engineer just to use >> ZFS... >> > > Just do ashift=12 and you're good to go. No need to analyze further. > > The reason I said that because in the future, *all* drives will have 4 > KiB sectors. Currently, many drives still have 512 B sectors. But when > one day your drive dies and you need to replace it, will you be able > to find a drive with 512 B sectors? > > Unlikely. > > That's why, even if your drives are currently of the 'classic' 512 B > ones, go with ashift=12 anyway. > > For SSDs, the situation is murkier. Many SSDs 'lie' about their actual > sector size, reporting to the OS that their sector size is 512 B (or 4 > KiB). No tool can pierce this veil of smokescreen. The only way is to > do research on the Internet. OK, so figure out what SSD you're using and Google to find the correct ashift? - Grant