On 04/25/2014 11:24 AM, Chris Murphy wrote:

On Apr 25, 2014, at 8:57 AM, Steve Leung <[email protected]> wrote:

I've got a 3-device RAID1 btrfs filesystem that started out life as 
single-device.

btrfs fi df:

Data, RAID1: total=1.31TiB, used=1.07TiB
System, RAID1: total=32.00MiB, used=224.00KiB
System, DUP: total=32.00MiB, used=32.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, RAID1: total=66.00GiB, used=2.97GiB

This still lists some system chunks as DUP, and not as RAID1.  Does this mean 
that if one device were to fail, some system chunks would be unrecoverable?  
How bad would that be?

Anyway, it's probably a high penalty for losing only 32KB of data.  I think this could use some 
testing to try and reproduce conversions where some amount of "system" or 
"metadata" type chunks are stuck in DUP. This has come up before on the list but I'm not 
sure how it's happening, as I've never encountered it.

As for how it occurred, I'm not sure. I created this filesystem some time ago (not sure exactly, but I'm guessing with a 3.4-era kernel?) so it's quite possible it's not reproducible on newer kernels.

It's also nice to know I've been one failed device away from a dead filesystem for a long time now, but better to notice it late than never. :)

Steve
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