From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC] relaxed barrier semantics Date: Tue, 27 Jul 2010 21:38:45 +0200 Message-ID: <20100727193845.GB8973@lst.de> References: <20100727165627.GA474@lst.de> <20100727175418.GF6820@quack.suse.cz> <20100727183546.GG7347@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Christoph Hellwig , jaxboe@fusionio.com, tj@kernel.org, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp To: Vivek Goyal Return-path: Received: from verein.lst.de ([213.95.11.210]:50026 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750936Ab0G0TjL (ORCPT ); Tue, 27 Jul 2010 15:39:11 -0400 Content-Disposition: inline In-Reply-To: <20100727183546.GG7347@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jul 27, 2010 at 02:35:46PM -0400, Vivek Goyal wrote: > IIUC, QUEUE_ORDERED_DRAIN will be set only for storage which either does > not support write caches or which advertises himself as having no write > caches (it has write caches but is batter backed up and is capable of > flushing requests upon power failure). More or less. We set it for scsi devices without the write cache enable (WCE) bit, which is only set it there is a volatile write cache that needs flushing. Some historic arrays used to set it despite having a non-volatile write cache, but that doesn't happen anymore with any of the modern ones I have access to.