On Thu, 25 Aug 2011 19:14:45 -0700 Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > mdadm -E /dev/sda --dump=foo > > Creates a sparse file image of /dev/sda named foo with a copy of the > metadata instance found by -E. > > When used in the opposite direction: > > mdadm -E foo --dump=/dev/sda > > ...can restore metadata to a given block device, assuming it is > identical size to the dump file. I like this functionality - I've thought about doing something like this before but never quite done it. I'm not convinced of the interface yet - especially the lack of checks. If it can be misused it will be misused and we should try to avoid that. Using a sparse file is probably a good idea - it removes the need to try to invent a format for storing non-consecutive metadata and recording the offset. dmraid has a --dump-metadata (-D) option which creates a directory and stores one file per device there. I like that as it make it easy to get everything in the right place. Maybe the arg to --dump could be a directory name to store dump files in ... but then we lose the pleasing symmetry of using the same command to dump and restore. But is that symmetry only pleasing to us and would it be confusing to new users? Suppose we did have a separate 'restore' function - what would it look like? An option to create? mdadm --create --restore=some-directory /dev/sda /dev/sdb Then the names of the dump files would need to indicate which array and which position in the array... And this would make it hard to restore the metadata to a single device. So probably just mdadm -E /dev/sda --restore=some-file would restore the metadata then report it?? Maybe keeping the old metadata as a backup. Or maybe drop the -E and just have '--dump' and '--restore' as top-level Misc options. It would be good if --restore would create a backup of the in-disk metadata if there is any - to "some-file.bak" maybe ?? So how about this: - allow --examine to work on a file. - new misc option --dump=foo will create directory foo and store an image of any metadata on each device listed - filename matches basename of device. - new misc option --restore=bar. For each device listed restore metadata from bar (if it is a file, in which case only one device) or bar/basename (if it is a directory). In either case if there is metadata on the device, save it to the file + ".bak". If ".bak" exists and there is metadata - abort. Does that seem reasonable? Thanks, NeilBrown -- 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
