From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ishtar.tlinx.org ([173.164.175.65]:35630 "EHLO Ishtar.sc.tlinx.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753431AbcLAEEo (ORCPT ); Wed, 30 Nov 2016 23:04:44 -0500 Message-ID: <583FA154.9050905@tlinx.org> Date: Wed, 30 Nov 2016 20:04:36 -0800 From: L A Walsh MIME-Version: 1.0 Subject: Re: default mount options References: <583E1488.7090502@tlinx.org> <6ecda11c-a993-3dd7-5b87-1947506953ff@sandeen.net> <583F2806.7080102@tlinx.org> <583F30C8.1000206@tlinx.org> <20161130221837.GH31101@dastard> In-Reply-To: <20161130221837.GH31101@dastard> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: Eric Sandeen , linux-xfs@vger.kernel.org Dave Chinner wrote: > For /some/ RAID controllers in /some/ modes. For example, the > megaraid driver that has been ignoring cache flushes for over 9 > years because in RAID mode it doesn't need it. However, in JBOD > mode, that same controller requires cache flushes to be sent because > it turns off sane cache management behaviour in JBOD mode... --- Lovely. For better or worse, none of my HW-based LSI-raid cards have been able to do JBOD. do JBOD. > This is a clear example of why "barriers" should always be on and > cache flushes always passed through to the storage - because we just > don't know WTF the storage is actually doing with it's caches. ---- When it comes to JBOD, its not so clear about where caching helps the most. Related -- wondering about how external journals would affect need for barriers. Haven't thought about it much, but it seems like one would get alot of bang-for-the-buck to put journals on SSD's. _If_ data written to SSD's becomes "safe" as soon as it is accepted by SSDs (not saying it *is*, but _if_ it is), then how "needed" is ordering of writes for rotating media -- apart from special use/need cases like apps maintaining their own data-integrity journals like DB's or such? Just wondering about how increasing use of SSD's might affect the need for barriers. Anyway, I have the illusion that I am mostly clear about current params (at least until my next disillusioning)... ;-) -l