From mboxrd@z Thu Jan 1 00:00:00 1970 From: jim owens Subject: Re: fdatasync/barriers (was : [Bug 421482] Firefox 3 uses fsync excessively) Date: Fri, 30 May 2008 14:48:22 -0400 Message-ID: <48404BF6.7070408@hp.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org To: Bryan Henderson Return-path: Received: from g5t0008.atlanta.hp.com ([15.192.0.45]:1161 "EHLO g5t0008.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752654AbYE3Ss2 (ORCPT ); Fri, 30 May 2008 14:48:28 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Bryan Henderson wrote: > A barrier doesn't say any particular data must sync-to-platter. I was told by a blkdev expert that there are barrier sequences that will do this... which probably means I asked the wrong questions. >>My further understanding is that some layers (and devices) >>have bugs and don't sync-to-platter. > > Those aren't bugs. They're conscious design choices, so the worst you can > say about them is they are design defects. The designer decided that the > user would be more upset by constant slowness than by exposure to data > loss in certain situations. Yes, even though the user's program or OS > explicitly requested sync-to-platter. But I agree the behavior should be > documented -- probably in every listing of the device's specifications. I know it is often a design choice for some system vendors to say they are posix compliant while not meeting the data integrity requirements just so they can win benchmarks. They don't document it, they hope they never get caught. Or do you think the specs don't require data to reach non-volatile storage? I'm not worried about devices since I can tell customers to buy ones that work. I'm worried if the kernel won't save user data. Trying to convince customers to move off proprietary systems and onto linux is a tough sell if we don't really protect their data. So I think I'll put finding a solution to fsync somewhere near the top of my own todo list. The large commercial users we (HP) want to pay my expenses would be a little unforgiving about fsync not working... and they keep packs of underfed lawyers in kennels :) jim