Re: Question: raid1 behaviour on failure

[Matthias Bodenbinder <matthias@bodenbinder.de>]

Am 20.04.2016 um 15:32 schrieb Anand Jain:
>> 1. mount the raid1 (2 disc with different size)
> 
>> 2. unplug the biggest drive (hotplug)
> 
>   Btrfs won't know that you have plugged-out a disk.
>   Though it experiences IO failures, it won't close the bdev.

Well, as far as I can tell mdadm can handle this use case. I tested that. I have an mdadm raid5 running. I accidentially unplugged a sata cable from one of the devices and the raid still worked. I did not even notice that the cable was unplugged until a few hours later. Then I plugged in the cable agaib and that was it. mdadm recovered the raid5 without any problem. -> This is redunancy!


> 
>> 3. try to copy something to the degraded raid1
> 
>   This will work as long as you do _not_ run unmount/mount.
 
I did not umount the raid1 when I tried to copy something. As you can see from the sequence of events: I removed the drive and immdiately afterwards tried to copy something to the degraded array. This copy failed with a crash of the btrfs module. -> This is NOT redundancy.

The ummount and mount operations are coming afterwards.

In a nutshell I have to say that the btrfs behaviour is by no means compliant with my understanding of redundancy.


Matthias