G'day, What is the best way to replace a fully-functional or minimally-failing (e.g. occasional bad sectors) disk in a live array whilst maintaining as much redundancy as possible during the process? It seems the standard way to replace a disk is to fail out the unwanted disk, add the new disk, then wait for the array to rebuild. However this means during the rebuild you've lost some or all of your redundancy, depending on the raid level of the array. This can be a significant issue, e.g. if you're replacing a 4 TB disk it could mean 10 to 20 hours or much more of heightened risk, depending on the rebuild bandwidth available. Another way would be to add in the new disk and grow the array, wait for the rebuild, then fail out and remove the old disk, shrink the array, and again wait for the rebuild. However once again you lose (some of) your redundancy from the time you've failed the old disk till the rebuild completes; again, potentially many hours. Unless there's some way of telling md to shrink the array off the unwanted device before removing it, and md is smart enough to retain full redundancy during the process? Another way might be to fail out the old drive, create a raid-1 between the old and new drives whilst doing some dance with dd and the original raid metadata and the new raid-1 metadata to make it appear the raid-1 was the original raid member, "re-add" the raid-1 device to the original raid, wait for the rebuild of both the raid-1 and the original raid, fail out the raid-1, do a reverse dd dance to make the new disk look like a primary member of the original raid, then "re-add" the new disk into the original raid. This would mean you only lose redundancy for the windows where the original raid has a failed-out member, i.e. seconds, if done properly. Is this method possible and, if sufficient care is taken, sensible? If it's possible, is this something that could or should be built into md to automate the process and perhaps reduce or completely eliminate the window of reduced redundancy? ...or, indeed, is this something that's already built into md and I need to do some significant self-flagellation with the clue bat? Cheers, Chris. -- 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
