Best way to break RAID5/6?

Best way to break RAID5/6?

[Casey Matson-deKay]

Hi all,

I'm new to the community, but love the work being done here. I'm an
embedded C developer and PCB designer, and would like to get involved
in btrfs.

I, like many, am frustrated at the mystery of raid5/6 functionality.
More for the learning experience than anything, I was wondering about
the best known methods to break raid5/6 in a test setup, in order to
understand the patterns by which it breaks, and eventually, play
around with the kernel code to understand what's going on more in
depth.

My initial thought, taking 3 USB drives, configuring them in RAID5,
and pulling one out during a write, seems a bit simplistic. Are there
known raid failure modes that would be more apt for learning and
understanding where the raid bugs lie in btrfs, and how to trigger and
explore them?

Thank you!

Casey

Re: Best way to break RAID5/6?

[Zygo Blaxell]

On Mon, Oct 05, 2020 at 06:46:53PM -0700, Casey Matson-deKay wrote:
> Hi all,
> 
> I'm new to the community, but love the work being done here. I'm an
> embedded C developer and PCB designer, and would like to get involved
> in btrfs.
> 
> I, like many, am frustrated at the mystery of raid5/6 functionality.
> More for the learning experience than anything, I was wondering about
> the best known methods to break raid5/6 in a test setup, in order to
> understand the patterns by which it breaks, and eventually, play
> around with the kernel code to understand what's going on more in
> depth.

Welcome to btrfs!

Here's a list of known raid5 bugs with background references:

	https://lore.kernel.org/linux-btrfs/20200627030614.GW10769@hungrycats.org/

> My initial thought, taking 3 USB drives, configuring them in RAID5,
> and pulling one out during a write, seems a bit simplistic. Are there

Just pulling one out is sufficient to hit the first bug:  some reads
fail in degraded mode.  

> known raid failure modes that would be more apt for learning and
> understanding where the raid bugs lie in btrfs, and how to trigger and
> explore them?
> 
> Thank you!
> 
> Casey