From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: Bug#624343: linux-image-2.6.38-2-amd64: frequent message "bio too big device md0 (248 > 240)" in kern.log Date: Mon, 02 May 2011 11:08:11 +0200 Message-ID: References: <20110427161901.27049.31001.reportbug@servo.factory.finestructure.net> <1304051980.3105.46.camel@localhost> <8739kyf53e.fsf@servo.factory.finestructure.net> <1304294457.2833.111.camel@localhost> <20110502102224.7787d6bd@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110502102224.7787d6bd@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 02/05/2011 02:22, NeilBrown wrote: > On Mon, 02 May 2011 01:00:57 +0100 Ben Hutchings wrote: > >> On Sun, 2011-05-01 at 15:06 -0700, Jameson Graef Rollins wrote: >>> On Fri, 29 Apr 2011 05:39:40 +0100, Ben Hutchings wrote: >>>> On Wed, 2011-04-27 at 09:19 -0700, Jameson Graef Rollins wrote: >>>>> I run what I imagine is a fairly unusual disk setup on my laptop, >>>>> consisting of: >>>>> >>>>> ssd -> raid1 -> dm-crypt -> lvm -> ext4 >>>>> >>>>> I use the raid1 as a backup. The raid1 operates normally in degraded >>>>> mode. For backups I then hot-add a usb hdd, let the raid1 sync, and >>>>> then fail/remove the external hdd. >>>> >>>> Well, this is not expected to work. Possibly the hot-addition of a disk >>>> with different bio restrictions should be rejected. But I'm not sure, >>>> because it is safe to do that if there is no mounted filesystem or >>>> stacking device on top of the RAID. >>> >>> Hi, Ben. Can you explain why this is not expected to work? Which part >>> exactly is not expected to work and why? >> >> Adding another type of disk controller (USB storage versus whatever the >> SSD interface is) to a RAID that is already in use. > > Normally this practice is perfectly OK. > If a filesysytem is mounted directly from an md array, then adding devices > to the array at any time is fine, even if the new devices have quite > different characteristics than the old. > > However if there is another layer in between md and the filesystem - such as > dm - then there can be problem. > There is no mechanism in the kernl for md to tell dm that things have > changed, so dm never changes its configuration to match any change in the > config of the md device. > While I can see that there might be limitations in informing the dm layer about changes to the md layer, I fail to see what changes we are talking about. If the OP were changing the size of the raid1, for example, then that would be a metadata change that needed to propagate up so that lvm could grow its physical volume. But the dm layer should not care if a disk is added or removed from the md raid1 set - as long as the /dev/mdX device stays online and valid, it should work correctly.