From: Andreas Dilger Subject: Re: Extent Depth Histogram Fsck Date: Tue, 26 Jun 2012 09:40:59 -0600 Message-ID: <55654AE5-17FE-44EC-B7FE-A8D5FAAB3560@dilger.ca> References: <0408C81F72528E40A0D3235A1F67FFC804A37F@SN2PRD0202MB144.namprd02.prod.outlook.com> Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Cc: "linux-ext4@vger.kernel.org" To: "Nelson, John R" Return-path: Received: from idcmail-mo1so.shaw.ca ([24.71.223.10]:61012 "EHLO idcmail-mo1so.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755973Ab2FZPlA convert rfc822-to-8bit (ORCPT ); Tue, 26 Jun 2012 11:41:00 -0400 In-Reply-To: <0408C81F72528E40A0D3235A1F67FFC804A37F@SN2PRD0202MB144.namprd02.prod.outlook.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2012-06-26, at 8:34 AM, Nelson, John R wrote: > What does the extent depth histogram mean? Is it a measure of something? > > like mine is > > > Extent depth histogram: 36010/81 This means that of all the extent-mapped files in the filesystem, 36010 files have an extent tree of depth 0 (i.e. they fit inside the inode) 81 files have an extent tree of depth 1 (i.e. there is a single index block) Typically, files larger than 4 * 128MB = 512MB need an index block, but if the maximum-sized extents cannot be allocated then an index block will be needed for smaller files. Only if you have very large files (> 40GB), or a very fragmented free space would you need more than a single level of index blocks. Cheers, Andreas