Hi Neil I brought this up in October but got no response - since you seem to be on a roll I thought I'd try again... Summary: Add a spare and 'mirror-fail' a device. The spare is synced with the to-be-removed device and any read errors are corrected from the remaining raid devices. Once synced, the to-be-removed device is failed and the spare takes its place. At no point is the array degraded. IMHO This one should be high on the todo list. Especially if it's a pre-requisite for other improvements to resilience. Right now, if a drive fails or shows signs of going bad then you get into a very risky situation. I'm sure most here know that the risk is because removing the failing drive and installing a good one to re-sync puts you in a very vulnerable position; if another drive fails (even one bad block) then you lose data. The solution involves raid1 - but it needs a twist of raid5/6 and it was discussed ages ago; see: http://arctic.org/~dean/proactive-raid5-disk-replacement.txt I think this is what was discussed: Assume md0 has drives A B C D D is failing E is new * add E as spare * set E to mirror 'failing' drive D (with bitmap?) * subsequent writes go to both D+E * recover 99+% of data from D to E by simple mirroring * any read failures on D when reading from md0 or mirroring D->E are recovered from reading ABC not E unless E is in sync. D is not failed out. (and it's these tricks that stops users from doing all this manually) * any md0 sector read failure on ABC can still (hopefully) be read from D even if not yet mirrored to E (also not possible if done manually) * once E is mirrored, D is removed and the job is done Personally I think this feature is more important than the reshaping requests; of course that's just one opinion after replacing about 20 flaky 1Tb drives in the past 6 months :) David -- "Don't worry, you'll be fine; I saw it work in a cartoon once..." -- 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
