Hi All, I write as I have some questions about dm-multipath, and there seems to be a dearth of good documentation available. To make things worse the official Wiki even contains self-conflicting information (compare: http://christophe.varoqui.free.fr/wiki/wakka.php?wiki=FAQ """supports root FS on multipathed SAN""" vs http://christophe.varoqui.free.fr/wiki/wakka.php?wiki=UsageFile """DM-MP cannot be run on either the root or boot device."""). I figured what better place to get answers than from the experts involved in actually developing the system :) What I would please like to get a clear understanding of is: 1) What are the software components and dependencies involved in the bare necessities of making dm-multipath work? I've reviewed the architectural diagrams (which are quite good), but am looking more specifically for answers to things like 'is there actually a hard technical necessity for udev in order to actually make dm-multipath to work, or is its presence more an artifact of the assumptions built-in to overall design of the system?' 2) Why exactly can't dm-multipath be used to multipath a root filesystem? What are the dependencies that can't be met by initrd? Why is dm-multipath different in this regard to any other block driver, eg md or LVM? OR 2) What exactly, specifically is required in order to have root on a multipath device? A high-level overview would probably be more useful than nitty-gritty of what entry to put in what file, at this point. I'm guessing that a solid answer to (1) above will probably answer (2) in the process. The reason for the request is that the seemingly desirable and obvious option of booting from a SAN on Linux is pretty much worthless if multipathing can't be used for root - your system is less safe than booting from some mirrored internal disks... Thanks in advance for any and all assistance and answers on this, Darryl Dixon http://www.winterhouseconsulting.com -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
