Re: Unexpected raid1 behaviour

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

[-- Attachment #1.1: Type: text/plain, Size: 2469 bytes --]



On 2017年12月17日 03:50, Dark Penguin wrote:
> Could someone please point me towards some read about how btrfs handles
> multiple devices? Namely, kicking faulty devices and re-adding them.
> 
> I've been using btrfs on single devices for a while, but now I want to
> start using it in raid1 mode. I booted into an Ubuntu 17.10 LiveCD and
> tried to see how does it handle various situations.
> The experience left
> me very surprised; I've tried a number of things, all of which produced
> unexpected results.
> 
> I create a btrfs raid1 filesystem on two hard drives and mount it.

Initial info like "btrfs fi df" will help us to dig this further.

> 
> - When I pull one of the drives out (simulating a simple cable failure,
> which happens pretty often to me), the filesystem sometimes goes
> read-only. ???

Please provide the kernel message.

> - But only after a while, and not always. ???
> - When I fix the cable problem (plug the device back), it's immediately
> "re-added" back. But I see no replication of the data I've written onto
> a degraded filesystem... Nothing shows any problems, so "my filesystem
> must be ok". ???

Needs extra info like "btrfs fi df"

> - If I unmount the filesystem and then mount it back, I see all my
> recent changes lost (everything I wrote during the "degraded" period).
> - If I continue working with a degraded raid1 filesystem (even without
> damaging it further by re-adding the faulty device), after a while it
> won't mount at all, even with "-o degraded".

Please provide kernel message too.
Although I doubt about the usefulness, it's still better than none.

Thanks,
Qu

> 
> I can't wrap my head about all this. Either the kicked device should not
> be re-added, or it should be re-added "properly", or it should at least
> show some errors and not pretend nothing happened, right?..
> 
> I must be missing something. Is there an explanation somewhere about
> what's really going on during those situations? Also, do I understand
> correctly that upon detecting a faulty device (a write error), nothing
> is done about it except logging an error into the 'btrfs device stats'
> report? No device kicking, no notification?.. And what about degraded
> filesystems - is it absolutely forbidden to work with them without
> converting them to a "single" filesystem first?..
> 
> On Ubuntu 17.10, there's Linux 4.13.0-16 and btrfs-progs 4.12-1 .
> 
> 


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 520 bytes --]