Re: [PATCH] btrfs: Allow more disks missing for RAID10

[David Sterba <dsterba@suse.cz>]

On Fri, Jul 26, 2019 at 07:41:41AM +0800, Qu Wenruo wrote:
> 
> 
> On 2019/7/26 上午2:37, David Sterba wrote:
> > On Thu, Jul 18, 2019 at 02:27:49PM +0800, Qu Wenruo wrote:
> >> RAID10 can accept as much as half of its disks to be missing, as long as
> >> each sub stripe still has a good mirror.
> > 
> > Can you please make a test case for that?
> 
> Fstests one or btrfs-progs one?

For fstests.

> > I think the number of devices that can be lost can be higher than a half
> > in some extreme cases: one device has copies of all stripes, 2nd copy
> > can be scattered randomly on the other devices, but that's highly
> > unlikely to happen.
> > 
> > On average it's same as raid1, but the more exact check can potentially
> > utilize the stripe layout.
> > 
> That will be at extent level, to me it's an internal level violation,
> far from what we want to improve.

Ah I don't mean to go the extent level, as you implemented it is enough
and an improvement.