Greetings! I have a mirror RAID with two devices (sdc1 and sde1). It's not a root partition, just a RAID with some data for services running on this server. (I'm running Debian Jessie x86_64 with a 4.1.18 kernel.) The RAID is listed in /etc/mdadm, and it has an external bitmap in /RAID . One of the devices in the RAID (sdc1) "fell off" - it disappeared from the system for some reason. Well, I thought, I have to reboot to get the drive back, and then re-add it. That's what I did. After the reboot, I saw a degraded array with one drive missing, so I found out which one , and re-added it back. Later, I noticed that I'm missing some data, and thinking about this situation led me to understanding what happened. After a reboot, the system tried to assemble my arrays; it found sdc1 first (the one that disappeared), assembled a degraded array with only this drive, and started it. When I re-added the second drive, I've overwritten everything that happened between those events. Now I'm trying to understand why this happened and what am I supposed to do in this situation to handle it properly. So now I have a lot of questions boiling down to "how should booting with degraded arrays be handled?" - Why did mdadm not notice that the second drive is "newer"? I thought there were timestamps in the devices and even in the bitmap!.. - Why did it START this array?! I thought if a degraded array is found at boot, it's supposed to be assembled but not started?.. At least I think that's how it used to be in Wheezy (before systemd?). - Googling revealed that if a degraded array is detected, the system should stop booting and ask for a confirmation in the console. (Only for root partitions? And only before systemd?..) - My services are not going to be happy either way. If the array is assembled but not run, they will have data missing. If the array is assembled and run, it's even worse - they will start with outdated data! How is this even supposed to be handled?.. Should I add dependencies on mounting a specific mountpoint in each service definition?.. Am I wrong in thinking that mdadm should have detected that the second drive is "newer" and assemble the array just like it was before, thus avoiding all those problems easily?.. Especially considering that the array on the "new" drive already consists of only one drive, which is "not as degraded" and would be fine to run, compared to the array on the "old" drive which was not stopped properly and only now learns about one of the drives missing? Maybe this behaviour is already changed in the newer versions?.. -- darkpenguin -- 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
