On Wed, 28 Apr 2010 18:19:45 -0700 Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > Neil Brown wrote: > > I'm not sure how this fits with imposing platform constraints. > > As platform constraints are closely tied to metadata types, it might be OK > > to have a metadata-specific tags (imsm=???) and leave to details to the > > metadata handler??? > > > > Dan: help me understand these platform constraints: what is the most complex > > constraint that you can think of that you might want to impose? > > At this point we really only need one constraint: prevent controller > spanning. If for example I take an existing imsm member off of ahci and > reattach it via a usb-to-sata enclosure mdadm needs a policy to prevent > associating that drive with anything on ahci. > > In a pinch this policy can be disabled, but you wouldn't want to rebuild > across usb or any other controller because the option-rom only talks > ahci and will mark the drive missing. > > So something like DOMAIN spanning=imsm, to tell mdadm to follow imsm > rules for this domain. Where 'spanning' is policy tag?? > Thanks. So we have two different ideas here. 1/ A given set of devices (paths) are all attached to the one controller. 2/ A given array is not allowed to span controllers The first statement is somewhat similar to a statement about sparegroups. It groups devices together is some way. The second is a policy statement, and is metadata specific to some extent. If I create a native-metadata array using the controller, then adding other devices from a different controller is a non-issue. It is only when an IMSM array is created that it is an issue (and then - only if the array is to be used for boot for for multi-boot). So the ARRAY line could have "exclusive-group=foo" where 'foo' is a group name similar to those used for 'spare-group=' But that isn't much fun for auto-detect and auto-assembly. Maybe we want to extend the 'auto' line. It gives policy on a per-metadata basis. Maybe: POLICY auto-assemble +1.x -all POLICY same-group imsm where 'same-group' means that all the devices in an array must be in the same spare-group. The 'domain' lines assign spare-groups to devices. Maybe "same-group" could be "same-$tag" so we could have different tags for different metadatas.... Is this working for anyone else, or have I lost the plot?? NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
