Re: Raid 5/6 Stability

[Gerald Hopf <gerald.hopf@nv-systems.net>]

Duncan wrote:
> So 4.4 is what I'd consider the magical raid56-stability release, and 
> I'd actually expect the wiki to be updated shortly thereafter, tho 4.4 
> is close enough now, and there have been no major raid56 bugs reported 
> in the 4.3 and 4.4 cycles, that arguably the wiki's raid56 status 
> could be updated now to reflect that.

I don't think the wiki should be updated to show raid5/6 as production 
ready. The state of raid5/6 is still bad:

1) you STILL can't even properly check for free space
btrfs fi usage /my/device
WARNING: RAID56 detected, not implemented
WARNING: RAID56 detected, not implemented
WARNING: RAID56 detected, not implemented
(btrfs-progs v4.3.1-31-g0ab3d31)

2) Scrub is STILL horribly slow. Basically takes forever, unusable for 
anything large (and who uses raid5/6 for something small?)

3) the already mentioned problem that unlike mdadm there is no email 
notification and no proper fault handling if problems occur

And all those 3 problems are unlikely to be fixed in kernel 4.4 cycle at 
least as far as I was able to observe.

However: I'm using btrfs-raid5 and I'm mostly HAPPY with it. But I 
consider my use experimental and I rsync my btrfs-raid5 contents to an 
external off-site backup storage bimonthly and I can live with a worst 
case of 2 months of data loss for what I'm storing on it. Would love to 
see 1+2+3 fixed though.

Gerald