On Thu, 02 Feb 2012 20:08:53 +0100 Asdo <asdo@xxxxxxxxxxxxx> wrote: > Hello list > > I removed sda from the system and I confirmed /dev/sda did not exist any > more. > After some time an I/O was issued to the array and sda6 was failed by MD > in /dev/md5: > > md5 : active raid1 sdb6[2] sda6[0](F) > 10485688 blocks super 1.0 [2/1] [_U] > bitmap: 1/160 pages [4KB], 32KB chunk > > At this point I tried: > > mdadm /dev/md5 --remove detached > --> no effect ! > mdadm /dev/md5 --remove failed > --> no effect ! What version of mdadm? (mdadm --version). These stopped working at one stage and were fixed in 3.1.5. > mdadm /dev/md5 --remove /dev/sda6 > --> mdadm: cannot find /dev/sda6: No such file or directory (!!!) > mdadm /dev/md5 --remove sda6 > --> finally worked ! (I don't know how I had the idea to actually try > this...) Well done. > > > Then here is another array: > > md1 : active raid1 sda2[0] sdb2[2] > 10485688 blocks super 1.0 [2/2] [UU] > bitmap: 0/1 pages [0KB], 65536KB chunk > > This one did not even realize that sda was removed from the system long ago. Nobody told it. > Apparently only when an I/O is issued, mdadm realizes the drive is not > there anymore. Only when there is IO, or someone tells it. > I am wondering (and this would be very serious) what happens if a new > drives is inserted and it takes the /dev/sda identifier!? Would MD start > writing or do any operation THERE!? Wouldn't happen. As long as md hold onto the shell of the old sda nothing else will get the name 'sda'. > > There is another problem... > I tried to make MD realize that the drive is detached: > > mdadm /dev/md1 --fail detached > --> no effect ! > however: > ls /dev/sda2 > --> ls: cannot access /dev/sda2: No such file or directory > so "detached" also seems broken... Before 3.1.5 it was. If you are using a newer mdadm I'll need to look into it. > > > > And here goes also a feature request: > > if a device is detached from the system, (echo 1 > device/delete or > removing via hardware hot-swap + AHCI) MD should detect this situation > and mark the device (and all its partitions) as failed in all arrays, or > even remove the device completely from the RAID. This needs to be done via a udev rule. That is why --remove understands names like "sda6" (no /dev). Then a device is removed, udev processes the remove notification. The rule ACTION=="remove", RUN+="/sbin/mdadm -If $name" in /etc/udev/rules.d/something.rules will make that happen. > In my case I have verified that MD did not realize the device was > removed from the system, and only much later when an I/O was issued to > the disk, it would mark the device as failed in the RAID. > > After the above is implemented, it could be an idea to actually allow a > new disk to take the place of a failed disk automatically if that would > be a "re-add" (probably the same failed disk is being reinserted by the > operator) and this even if the array is running, and especially if there > is a bitmap. It should so that, providing you have a udev rule like: ACTION=="add", RUN+="/sbin/mdadm -I $tempnode" You can even get it to add other devices as spares with e.g. policy action=force-spare though you almost certainly don't want that general a policy. You would want to restrict that to certain ports (device paths). > Now it doesn't happen: > When I reinserted the disk, udev triggered the --incremental, to > reinsert the device, but mdadm refused to do anything because the old > slot was still occupied with a failed+detached device. I manually > removed the device from the raid then I ran --incremental, but mdadm > still refused to re-add the device to the RAID because the array was > running. I think that if it is a re-add, and especially if the bitmap is > active, I can't think of a situation in which the user would *not* want > to do an incremental re-add even if the array is running. Hmmm.. that doesn't seem right. What version of mdadm are you running? Maybe a newer one would get this right. Thanks for the reports. NeilBrown > > Thank you > Asdo > > > -- > 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
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