From owner-freebsd-fs@FreeBSD.ORG Mon Apr 2 11:37:53 2012 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 2D3EB106566C for ; Mon, 2 Apr 2012 11:37:53 +0000 (UTC) (envelope-from alexander@leidinger.net) Received: from mail.ebusiness-leidinger.de (mail.ebusiness-leidinger.de [217.11.53.44]) by mx1.freebsd.org (Postfix) with ESMTP id C66AC8FC14 for ; Mon, 2 Apr 2012 11:37:51 +0000 (UTC) Received: from outgoing.leidinger.net (p4FC43A0F.dip.t-dialin.net [79.196.58.15]) by mail.ebusiness-leidinger.de (Postfix) with ESMTPSA id 9F8978446D3; Mon, 2 Apr 2012 13:37:28 +0200 (CEST) Received: from webmail.leidinger.net (webmail.Leidinger.net [IPv6:fd73:10c7:2053:1::3:102]) by outgoing.leidinger.net (Postfix) with ESMTPS id DBF0D2037; Mon, 2 Apr 2012 13:37:25 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=leidinger.net; s=outgoing-alex; t=1333366646; bh=7fVgs0A7jrnrReuenQjvICE3RJYGzLt8vGS1Qe4nUuc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=tzGrFqqcaN+wtUy+hqKv5k1jkdeEx703KGXBKVzYnuAGGw7P7UihUXBREUDuZi9jn nDN1baa4F80BbgIkUAx6rLYazasi76oV2ChxvX+a/+wJs0DEIPTTdK1i3DpkbrvPQU HqRMur6hLDSMkZdmBDheyfzTmzQKXQU6tWgcninDg0e2RI1exNkehqSowcEBIFYUZt khhji4xh+mfa9G40xON/j5mw69BTq6PvTdvNHHwXaWHFj5rnFOpyK5jdwc8lHmwfHD SjZusZAeJ5vwjpcIukKIaIr+1co2ayVFwLPz0CVo6hbgIcuJrM5Y7RlfMrt4F/BH5j vJTu4NekTR5Yw== Received: (from www@localhost) by webmail.leidinger.net (8.14.5/8.14.4/Submit) id q32BbN5H005065; Mon, 2 Apr 2012 13:37:23 +0200 (CEST) (envelope-from Alexander@Leidinger.net) X-Authentication-Warning: webmail.leidinger.net: www set sender to Alexander@Leidinger.net using -f Received: from 195.46.238.197 ([195.46.238.197]) by webmail.leidinger.net (Horde Framework) with HTTP; Mon, 02 Apr 2012 13:37:23 +0200 Date: Mon, 02 Apr 2012 13:37:21 +0200 Message-ID: <20120402133721.Horde.KOqoS5jmRSRPeY9xDWLhHWA@webmail.leidinger.net> From: Alexander Leidinger To: Taylor References: <45654FDD-A20A-47C8-B3B5-F9B0B71CC38B@enone.net> <20120324174218.00005f63@unknown> In-Reply-To: User-Agent: Internet Messaging Program (IMP) H4 (5.0.19) Content-Type: text/plain; charset=ISO-8859-1; format=flowed; DelSp=Yes MIME-Version: 1.0 Content-Disposition: inline X-EBL-MailScanner-Information: Please contact the ISP for more information X-EBL-MailScanner-ID: 9F8978446D3.A29CC X-EBL-MailScanner: Found to be clean X-EBL-MailScanner-SpamCheck: not spam, spamhaus-ZEN, SpamAssassin (not cached, score=-0.686, required 6, autolearn=disabled, AWL -0.65, DKIM_SIGNED 0.10, DKIM_VALID -0.10, DKIM_VALID_AU -0.10, TW_ZF 0.08, T_RP_MATCHES_RCVD -0.01) X-EBL-MailScanner-From: alexander@leidinger.net X-EBL-MailScanner-Watermark: 1333971451.06643@kjO8yMQ1Bd3xzrpTpqV1rQ X-EBL-Spam-Status: No Cc: freebsd-fs@freebsd.org Subject: Re: ZFS extra space overhead for ashift=12 vs ashift=9 raidz2 pool? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Apr 2012 11:37:53 -0000 Quoting Taylor (from Sat, 24 Mar 2012 11:41:20 -0700): > Alex, > > Thank you for your response. I'm not particularly concerned about > the overhead of file fragmentation, > as most of the space will be take by fairly large files (10's of GiB). > > My original question concerned the amount of space reported > available by zfs for a > freshly-created *empty* raidz2 filesystem. > > To re-iterate, I find 2.79TiB more space available with ashift=9 > (49.62 TiB) vs ashift=12 (46.83TiB) > for a new 3.64TiB 16-disk raidz2 pool. I do not know for the actual amount, but at least some overhead is not surprising to me. You have some meta data in ZFS (file permissions, ACLs, checksums, ...). This meta data should be more often much less than 4k in size, but you need to allocate at least one block for this meta data. If we assume (worst case) that most of the time the meta data would fit into 512 byte but you always use a 4k sector, it should be clear that you use 8 times more space on the disk for each meta data unit, than necessary. Bye, Alexander. -- Let me put it this way: today is going to be a learning experience. http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7 http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137