On Sunday May 25, k@kaisung.com wrote: > Hi Neil, > I should probably elaborate a little more on my envisioned > setup. I'd like to setup a RAID array using shared disks, then run LVM > on top of the RAID array to carve out logical volumes. The logical > volumes would be used by one node at a time (no data sharing). For both > nodes to access the same LVM metadata, they must both activate the RAID > array. It seemed like someone had done something similar here: > > http://marc.theaimsgroup.com/?l=linux-raid&m=98834623209225&w=2 > > Concerning the checksums, I was referring to the checksum output when I > run mdadm --examine on a RAID disk. I thought that was a checksum of all > the data blocks of the disk, but I guess not? So, basically the only > time you can guarantee a RAID array is consistent is once it's been > deactivated and the dirty flag cleared in the superblock? It isn't clear what the auther of the refered mail is really doing, but I stand by my position that this cannot work. A raid array is not just a bunch of discs. It is also a controller. With Linux Soft raid, that controller is a computer running Linux. In the case of hardware raid, it might be an embeded system on a board somewhere. But there is still a single controller. It probably would not be impossible to arrange a soft RAID system where separate controller (Linux systems) could co-operate and manage separate parts of the array, but it would be a lot of work. The checksum is the checksum of the superblock, not the whole array. Yes. Yoo can only guarantee consustency if the dirty flag is clear. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
