I cannot find information about this topic on the web. Reducing the size of the components of an md array keeps the superblock 1.0 at the same position (which avoids data corruption and maybe is required for md to find it). However how can one then reduce the size of the underlying device without losing the superblock? In an array with redundancy re-addind reduced components one after the other is a rather safe solution, I suppose, but it is time consuming. Would it be possible to update the superblock version by doing that, either by mixing different superblock versions by giving --metadata with --add or by modifying the partitions defining the re-added components so that the new devices start at the right offset for a superblock 1.2 (and later using the following solution, re-creating the array with the original partitions and a 1.2 superblock at the right offset with --data-offset)? Re-creating all components after a reduction of the underlying devices seems possible by using --assume-clean. What to look for to avoid data loss? mdadm already supports enlarging a 1.0 component, which requires moving the superblock, so the code to reduce one would probably not require much efforts. Could it be added in the future? I would like to attempt to move the superblocks 1.0 manually, but I lack some information: 1) Should the reserved space before the superblock be moved along? 2) Is there metadata inside a superblock 1.0 to update after the move (that another program would not correct automatically)? 3) How is the superblock detected? Is there only one position possible for a given chunk size on a given component size? Should the remaining (padding) sectors of the underlying device be zeroed? Thanks -- 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
