From owner-freebsd-fs@FreeBSD.ORG Mon Sep 20 21:20:39 2010 Return-Path: Delivered-To: freebsd-fs@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id EFF2D106566B for ; Mon, 20 Sep 2010 21:20:38 +0000 (UTC) (envelope-from jamie.ostrowski@gmail.com) Received: from mail-iw0-f182.google.com (mail-iw0-f182.google.com [209.85.214.182]) by mx1.freebsd.org (Postfix) with ESMTP id AFD728FC15 for ; Mon, 20 Sep 2010 21:20:35 +0000 (UTC) Received: by iwn34 with SMTP id 34so5387067iwn.13 for ; Mon, 20 Sep 2010 14:20:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:date:message-id :subject:from:to:content-type; bh=XYBCqP87gelRk+hSqM+XaaRKWRcE44XqB7a4n79Phbo=; b=LTSJ83BHF/Ld286D374IaVH0EktMfR3o2k42c6P9BuETZYLnYZwe5ZlLHT2cHh5kWG 28ptOSjiteRA/bKkjDNI2oniNkqxU7EG40RhggYbs3afH7VKTF/z//GbNGtlrFnzS38l Nltuh1ge41srnuWBE7TuWYjqnsWWfJHv42VUY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=qIf5Aw70lVcSx8OgzQDDu0MVpNinLFY1lRIbGexrH6d6MPUd/TpPAskmlA6h9RtEZ9 QNsx7pby32H2BC75dgyhxDeJpBpwAHBlZnkZ5OBMhzAk146AiRLjupVbXW7Nb+b2G5Zw HBx8aYQhJ0+TGqtNWgexunh3Jh77l5v028sPw= MIME-Version: 1.0 Received: by 10.231.190.149 with SMTP id di21mr10672241ibb.166.1285016201513; Mon, 20 Sep 2010 13:56:41 -0700 (PDT) Received: by 10.231.206.145 with HTTP; Mon, 20 Sep 2010 13:56:41 -0700 (PDT) Date: Mon, 20 Sep 2010 15:56:41 -0500 Message-ID: From: Jamie Ostrowski To: freebsd-fs@FreeBSD.org Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: Subject: understanding block distribution in UFS2 filesystems 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, 20 Sep 2010 21:20:39 -0000 I thought I understood how block distribution in UFS2 filesystems work, until I tried running dumpfs on one of my filesystems. The output really confused me, and the man page doesn't get into detail in explaining the output. Can anyone explain why I am seeing references to the same "free blocks" in different cylinder groups? I thought that the block numbers were unique across the entire filesystem, but from the output of dumpfs, I see references to free blocks 0-7 in almost every cylinder group. So are the blocks that are in each cylinder group numbered start over with a new block 0 in each cylinder group? In other words, which picture below is true, A, or B: Cylinder group 0: Uses blocks 0-4000 Cylinder group 1: Uses blocks 4001-8000 Cylinder group 2: Uses blocks 8001-12000 OR -- B: Cylinder group 0: Uses blocks 0-4000 Cylinder group 1: Uses blocks 0-8000 Cylinder group 2: Uses blocks 0-7000 (IE in that sense blocks must be referenced not only by the block number but by the cylinder group they are in) I sure hope so, otherwise I am completely lost on this dumpfs output. Thanks to anyone who can help clear up some of this confusion. - Jamie