On 01/16/2017 08:46 PM, Ken Goods wrote: > Hi all, > Just a quick question. I've been setting up a (iscsi) LUN and want to > create an LVM PV on it. > > The docs I have read are somewhat conflicted. Some say that the > underlying devices should be filtered, however according to comments in > lvm.conf it says that if multipath_component_detection is enabled, "LVM2 > will ignore devices used as component paths of device-mapper multipath > devices". > > So filtering is no longer necessary with LVM2? > The multipath component detection is an automatic filter in LVM2 (if enabled with devices/multipath_component_detection=1 in LVM configuration - that is used by default). So in this case you don't need to set up devices/global_filter (or devices/filter) manually. LVM will filter multipath components automatically by looking at the device stack and if it detects that there's a multipath device on top of certain set of devices, such devices are assumed as multipath components and they're filtered automatically. Of course, for this automatic filter to work correctly, you also need to have your multipath correctly configured - LVM doesn't know that the devices are multipath components unless there's multipath device already set up and running on top of those components. However, there's one improvement in this detection if you use devices/external_device_info_source="udev" in your LVM configuration (this is not used by default yet). In this case, LVM reads information from udev database which in turn has this information about multipath components directly from multipath and that one takes this information from its own configuration (the component WWID list in multipath's configuraton) - so in this case you don't even need to have multipath device set up yet on top of multipath components for LVM to detect multipath components properly. But usually, if your system is properly configured, you always have multipath device set up and running on top of multipath components. -- Peter _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
