From mboxrd@z Thu Jan 1 00:00:00 1970 From: Heinz.Mauelshagen@t-online.de (Heinz J . Mauelshagen) Subject: Re: [lvm] [christophe.varoqui@free.fr: dm multipath target] Date: Tue, 19 Aug 2003 14:35:52 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20030819143552.K8420@sistina.com> References: <20030819073926.GA423@fib011235813.fsnet.co.uk> <20030819094838.F8428@sistina.com> <1061283871.3f41e81f8226b@impt3-2.free.fr> <20030819115110.I8420@sistina.com> <1061290087.3f4200678f811@impt2-2.free.fr> Reply-To: mauelshagen@sistina.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mailout05.sul.t-online.com ([194.25.134.82]:47013 "EHLO mailout05.sul.t-online.com") by vger.kernel.org with ESMTP id S270416AbTHSMmV (ORCPT ); Tue, 19 Aug 2003 08:42:21 -0400 In-Reply-To: <1061290087.3f4200678f811@impt2-2.free.fr>; from christophe.varoqui@free.fr on Tue, Aug 19, 2003 at 12:48:07PM +0200 List-Id: linux-scsi@vger.kernel.org To: christophe.varoqui@free.fr Cc: mauelshagen@sistina.com, mge@sistina.com, linux-scsi@vger.kernel.org On Tue, Aug 19, 2003 at 12:48:07PM +0200, christophe.varoqui@free.fr wrote: > Selon "Heinz J . Mauelshagen" : > > > Ghosts should report EIO in case of an unstarted LUN anyway ? > > In case they are started they are supposed to report EPERM on IO because > > they don't support any. > > > All I can say is that it blocks pvscan for a looong time. I havn't had the > patience to see if it finaly abords. :( Then set up a device filter in lvm.conf to avoid access. > > > Even reporting EPERM in both cases would be sufficient, because IO > > will never make it through a ghost. Blocking makes no sense to me at all. > > > That's the vendor-specific issue I talk about : other controlers certainly > return errors, other activate the path on IO submission (with or without > penalty). HSV simply blocks. Well, error-reporting and handling in Linux is "weak" anyway. More 2.7 work (as kernel hackers know) including standards for vendor specific drivers ITR. > > > There's various "flavours" where to put multipath into the io chain. > > Kernel hacker conclusion is in device-mapper. > > > No problem with that :) > > > Multipathing is a device-mapper target and therefore offers a general kernel > > service to be used by arbitrary applications. > > LVM2 is the one from us supporting that in the future. > > > Does it mean the multipath tools from you will be packaged in the lvm compound > binary, or as an independant set ? In the LVM2 binray. > > > Other LVM applications are free to implement a different model. > > > > Device-mapper has no clue of volume management metadata. LVM2 has. > > > > We need better device recovery in Linux (which will happen in the Linux 2.7 > > series later). PV UUIDs enable LVM2 to discover PVs. > > > Yes, but does it mean _your_ multipath tools will need PV UUIDs ? Yes. > Will these tools be relevant outside of LVM2 volume management scope, as for > them to become "standard" ? No restriction that the part of the LVM2 lib could, it's LGPLed. > > > I much rather prefer a cleaner ghosts implementation not blocking > > critical applications. > > > The ghost behaviour being vendor-specific, policy belongs to userspace. If the > vendor says the ghost does not respond to IO, then it's up to userland to > instruct the kernel to not submit IO to it (ie set device mappings). Sorry, this sounds like a workaround mess with arbitrary vendor specific drivers and their behaviours. As said: we can filter such devices out in LVM2. > As you plan to package a set of userspace tools for multipath management, you > should allow plugins implementing those policies. Overkill because of missing standard(s). I much rather prefer enhanced and correct error reporting. And as said above: no need because we can easily filter out device nodes which don't allow (IO) access. > > regards, > cvaroqui -- Regards, Heinz -- The LVM Guy -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Heinz Mauelshagen Sistina Software Inc. Senior Consultant/Developer Am Sonnenhang 11 56242 Marienrachdorf Germany Mauelshagen@Sistina.com +49 2626 141200 FAX 924446 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-