From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: Re: Mdadm, udev and fakeraid? Date: Sat, 23 Apr 2011 18:45:51 +1000 Message-ID: <20110423184551.7bb437de@notabene.brown> References: <20110405162008.5f2c48fe@notabene.brown> <20110418103852.2ead1a69@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Dan Williams Cc: Seblu , linux-raid@vger.kernel.org List-Id: linux-raid.ids On Fri, 22 Apr 2011 19:37:40 -0700 Dan Williams wrote: > On Sun, Apr 17, 2011 at 5:38 PM, NeilBrown wrote: > > As has been mentioned elsewhere, mdadm only recognised IMSM arrays = on > > machines with IMSM hardware. =A0I'm not entirely happy about this a= nd may well > > change it. >=20 > I have trouble answering the "least surprise" question in this area. >=20 > Is it more surprising to go into your BIOS, explicitly turn off raid > support and still see raid devices showing up? Is the "RAID support has been explicitly turned off" state visible from= a running kernel? or is it indistinguishable from "platform does not have= RAID support"? >=20 > Or is it more surprising to take a raid array from a raid enabled > system to raid disabled system and wonder why things won't assemble? >=20 > For safety I think it is better if mdadm not perform operations that > might be incompatible with the platform option-rom. But if you need > to recover to a usb attached drive, or some other > platform-incompatible configuration, you can use the environment > variable in a pinch. There are 3 interesting cases: create, assemble, examine. (grow might be interesting too, but for now it would be confusing). I am perfectly happy for 'create' to be arbitrarily hard if platform su= pport is not available. One is unlikely to want to create an array in that c= ase anyway. I think 'examine' should always show whatever it can, which is the case= for 3.2.1. Possibly it should also give a warning about any difficulty th= at might be experienced in assembling the array. Assemble in the interesting case. The law of least surprise requires i= t to either work or give a good error message. Your suggestion that it poss= ibly should not work in some cases seems defensible, so at least a very clea= r error message would be good. As for how to over-ride the default caution - I would prefer --force to achieve it rather than requiring an environment variable. I would poss= ibly accept --force-platform (or similar) but I think --force should be suff= icient. What think you? Thanks, NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html