From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH 06/12] Make multipath add wwids from kernel cmdline mpath.wwids with -A Date: Thu, 03 Jul 2014 13:05:37 +0200 Message-ID: <53B53901.3050606@suse.de> References: <1404105243-5071-1-git-send-email-bmarzins@redhat.com> <1404105243-5071-7-git-send-email-bmarzins@redhat.com> <53B3A0BA.9040502@suse.de> <20140702194816.GF10438@dhcp80-209.msp.redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; Format="flowed" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20140702194816.GF10438@dhcp80-209.msp.redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: dm-devel@redhat.com List-Id: dm-devel.ids On 07/02/2014 09:48 PM, Benjamin Marzinski wrote: > On Wed, Jul 02, 2014 at 08:03:38AM +0200, Hannes Reinecke wrote: >> On 07/01/2014 09:22 PM, Christophe Varoqui wrote: >>> Hannes, >>> >>> would you Ack this one, or do you have some other idea for this in >>> your tree ? >>> >> Sigh. The whole multipath / systemd / dracut integration >> is _a mess_. >> The main problem is that RH and SUSE treat multipath handling differentl= y. >> (From what I can see. I've still a hard time to understand how >> multipath booting works with RH. So there might be errors.) >> >> RH is taking a restrictive approach, ie it'll allow only configured >> multipath devices during boot. IE it'll accept only devices present >> in '/etc/multipath/wwids' for booting. So when coming across a new >> wwid multipath won't be setup there, so of course they'll need an >> additional parameter for that. > > That's not strictly true. multipathd will happily create a multipath > device on top of any valid scsi devices it finds, but unless those > devices are in /etc/multipath/wwids, other components, like lvm won't > know to leave them alone. This actually isn't an issue during the > initramfs boot stages because lvm doesn't do autoactivation there. > > So, if the device appears in the initramfs portion of boot, we're great. > > The specific issue that prompted this goes like this: > > - The iscsi initiator is not setup to run in the initramfs on install > - Storage is added to the system that makes up a working LV > - Once the machine boots up, and is past the initramfs, the iscsi > initiator starts up and discovers the devices. > - Multipath races with lvmetad and loses > - Now you have a LV built on top of a single path device, instead of > being multipathed (The LV is on top of a partition of the path > device, so reassign_maps doesn't work on it) > > If you tell the redhat installer that you want to use multipath, this > causes problems, since it can't disassemble the an arbitrary stack of > virtual devices. Eventually, we'll fix that issue, and this won't > matter anymore, because it will just be able to disassemble the virtual > device stack, and rerun multipath, to make everything autoassemble in > the correct order. > Hmm. Similar to what I've seen here when booting with multipath = enabled and an empty '/etc/multipath/wwids' file. We're having an udev rule calling 'multipath -u' to check if the = device is eligible for multipathing. If so it'll set the various = udev properties to keep LVM and others from working with that device. But as 'multipath -u' is be checking /etc/multipath/wwids it will = always report 'not a multipath device'. So I would be perfectly happy with 'multipath -u' _not_ checking = /etc/multipath/wwids (or have a switch for doing so). Anyway. There is actually a slight inconsistency with the above = approach: Multipath is _not_ setup for autoconfiguration; from my = understanding this was exactly why /etc/multipath/wwids was = introduced in the first place. LVM, on the other hand, is trying to do autoconfiguration. Why? I would set either both to autoconfiguration or none. If I want something different I need to configure the system. Can you clarify what the intended usage for /etc/multipath/wwids is? I was under the impression that it's been introduced to keep multipath from accepting unconfigured devices ... Cheers, Hannes -- = Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: J. Hawn, J. Guild, F. Imend=F6rffer, HRB 16746 (AG N=FCrnberg)