Re: BTRFS RAID5 filesystem corruption during balance

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Duncan <1i5t5.duncan <at> cox.net> writes:

> FWIW, btrfs raid5 (and raid6, together called raid56 mode) is still 
> extremely new, only normal runtime implemented as originally introduced, 
> with complete repair from a device failure only completely implemented in 
> kernel 3.19, and while in theory complete, that implementation is still 
> very immature and poorly tested, and *WILL* have bugs, one of which you 
> may very well have found.
> 
> For in-production use, therefore, btrfs raid56 mode, while now at least 
> in theory complete, is really too immature at this point to recommend.  
> I'd recommend either btrfs raid1 or raid10 modes as more stable within 
> btrfs at this point, tho by the end of this year or early next, I predict 
> raid56 mode to have stabilized to about that of the rest of btrfs, which 
> is to say, not entirely stable, but heading that way.
> 

Hi Duncan,

Thanks for your reply.

I was under the impression that RAID5/6 was considered quite stable in the
more recent kernels, hence my use of the 3.19 kernel and the upgraded
btrfstools.  It's obvious that I was wrong in this assumption and maybe
btrfs RAID5 should be labeled as experimental code then.

A balance operation is supposed to be safe as it makes a copy of each file,
rewrites it, distributing the data over all devices and only then deletes
the original file?  This should never lead to kernel deadlocks ...
Having a corrupted filesystem after a reboot due to this is even more
worrisome, I think.  And worst of all are the btrfs kworker crashes.  Kernel
code should never crash IMHO, but maybe I'm slightly naive here ;-) .

Anyways, lots of lessons learned, and I'll see if I can repair the
filesystem as described in https://btrfs.wiki.kernel.org/index.php/Btrfsck
If it doesn't work, I'll simply start over with an alternative filesystem.

Regards,
Jan


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