On 04/21/2016 01:15 PM, Matthias Bodenbinder wrote:
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!
Yep. I meant to say its a bug in btrfs that it won't know
about the missing device (after mount). Pls do test the hot
spare patch set it has few first steps (yep not a complete)
to handle the failed device while FS is mounted.
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.
A known issue.
Your testing / validating of hot spare patch set will help.
Thanks, Anand
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