I've got myself into the babit of comparing the output from "cat /proc/mdstat" and "mdadm -Esbv" to see if there's any old md metadata floating around on disks I'm about to use before using them. Just as a precaution. If I find any then I --zero-superblock the disk first before re-using it, just to prevent myself getting caught out by events like this. Rgds, John On Wed, Jul 1, 2009 at 3:43 AM, Roger Heflin<rogerheflin@xxxxxxxxx> wrote: > Molinero wrote: >> >> Hi all >> >> I've lost quite a lot of data on my /home raid partition and I'm wondering >> what exactly I did to make it happen. I'd like to know so something >> similar >> won't happen in the future. >> >> I'm pretty much a raid newbie. I setup raid1 on my home server and I'm >> guessing that something like this happened. Please tell me if it's >> possible. >> >> * Some time ago I did something to have one device fail which resulted md3 >> in having only 1 device. >> * Time went by without me noticing (because I suck) >> * An update broke my raid setup and gave me a kernel panic (because I >> suck). >> Didn't put the mdadm and raid hooks in mkinitcpio.conf >> * Booted a live-cd, mounted the drives and chrooted back into the system >> and >> fixed the mkinitcpio.conf >> * Rebooted and noticed that md3 was running with only 1 device >> * Added sdb4 to md3 and it then read 1 device with 1 spare >> * cat /proc/mdstat started to say "recovery" >> * All data from approx. 1 year is gone >> >> I guessing that the old (not updated) device was set as "master" and the >> data on the drive (containing newer data) was overwritten by data on the >> old >> device - is this plausible? > > If the old device was brought up as md3 and had dropped out months ago, the > data would now be the data that existed when that disk dropped off. And > when a device drops out, there is no mark on that device marking it as bad > since the typical reasons for the device dropping off are that it is not > longer talking. And sometimes mirrors are intentionally broken for > various reasons to preserve a copy for one reason or another such as to be > able to back out of a serious OS upgrade that did not go well quickly. > > If you added the current device as a spare it would have copied the data > from the old device over the current device. > > That is one thing that would make 3+ disk raid5 a bit more resistant to > this, with a dropped off disk you could not start the array with only the > dropped device, and with all 3, 2 of the devices will know the 3rd was > dropped at some time in the past, and with any 2 on of those devices would > believe the other one was marked bad. > > > -- > 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 > -- 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
