So for DMRAID and mapper partition types, there is no "start" file in sysfs. If you use the old ioctl HDIO_GETGEO it returns the start as 0. Trying to use the BLKPG_GET_PARTITION on the physical drive itself but no system I tried that IOCTL on had any support (but that IOCTL isn't documented anywhere that I see - examples only set the partition number field) .. I'd really rather use it on the partition device that is opened already. So the question is, how do you get the starting LBA of a given partition for mapper type devices (can't assume the file system will be known or even exist)?