From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([65.50.211.133]:52493 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750778AbdCHQJZ (ORCPT ); Wed, 8 Mar 2017 11:09:25 -0500 Date: Wed, 8 Mar 2017 07:56:02 -0800 From: Christoph Hellwig Subject: Re: Significantly longer fallocate times with Flag Unwritten Extents disabled Message-ID: <20170308155602.GE4353@infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Bill McDuck Cc: linux-xfs@vger.kernel.org On Mon, Mar 06, 2017 at 12:02:01PM +0000, Bill McDuck wrote: > Hello. > > I have been testing the performance of XFS with "Flag Unwritten > Extents" enabled and disabled. Why do you disable it? It's been part of the defauly on feature set for a decade, and manually disabling it will make you run into completely untested code. There is a reason it's mandatory for v5 file systems. > > For security reasons I know XFS flags all unwritten extents by > default, so that uninitialized disk space cannot be read by the user. > In my application I actually want to have access to this uninitialized > disk space. I have been modifying the superblocks using xfs_repair to > enable this functionality. Don't do that, it's not supported for a reason.