Hello, I just signed up for this mailing list to discuss the following, unexpected behavior: Situation: Raid6 with 6 discs. For some reasons, which are unimportant, I had replaced a disc before, which was fully functional. This disc was never changed or written to in between. Today I replugged this particular disc additionally as 7th disc to the server (cold plug, server was switched off). Unexpectedly mdadm broke up my fully synced raid6 and now syncs back to this old disc dropping one of the newer discs from the raid. This might be because it has its uuid still stored with higher rank than the newer disc or because the old disc got a lower sdX slot. I don't know that in detail. Anyway, I wouldn't expect mdadm to act like this. It might use the old, now plugged in again disc as hot spare or ignore it at all. But it shouldn't break a fully synced raid. I have reduced redundancy for about 24 hours now - without any rational reason. Especially as this isn't a usual use case. In general, you'd only replace broken discs. So this behavior makes even less sense to me, because it shouldn't try to use a potentially broken disc. Is this a bug? Or maybe something the developer's haven thought of, or is this just unprecedented? The kernel version is 4.14 mainline on Ubuntu 16.04 LTS. Regards, Matthias -- 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
