On Tue, Mar 07, 2017 at 09:35:56AM +0800, Qu Wenruo wrote: > At 03/07/2017 08:36 AM, Adam Borowski wrote: > > Not so for -draid5 -mraid1, unfortunately: > > Unfortunately, for raid5 there are still unfixed bugs. > In fact, some raid5/6 bugs are already fixed, but still not merged yet. > > > [/mnt/btr2/scratch]# btrfs fi us /mnt/vol1 > > Data,RAID5: Size:2.02GiB, Used:1.21GiB > > /dev/loop0 1.01GiB > > /dev/loop1 1.01GiB > > /dev/loop2 1.01GiB > > [/mnt/btr2/scratch]# umount /mnt/vol1 > > [/mnt/btr2/scratch]# losetup -D > > [/mnt/btr2/scratch]# losetup -f rb > > [/mnt/btr2/scratch]# losetup -f rc > > So you're pulling out first device. > In theory, it should be completely OK for RAID5. > And the degradable check follows it. > > > [/mnt/btr2/scratch]# mount -noatime,degraded /dev/loop0 /mnt/vol1 > > [/mnt/btr2/scratch]# btrfs fi us /mnt/vol1 > > Data,RAID5: Size:2.02GiB, Used:1.21GiB > > /dev/loop0 1.01GiB > > /dev/loop0 1.01GiB > > /dev/loop1 1.01GiB > > Two loop0 shows up here, which should be detected as missing. > > So it should be a btrfs-progs bug, and it'll be much easier to fix than > kernel. Alas, it's not merely a display bug, mounting is enough. > > Write something, mount degraded again. Massive data corruption, both on > > plain reads and on scrub, unrecoverable. > > Yep, same thing here. > And you'll be surprised that even 2 devices RAID5, which is the same as > RAID1(parity is the same as data), can still cause the problem. > > So, RAID5/6 definitely has problem in degraded mode. > While I prefer to focus on normal RAID5/6 bug fix first, and until we solve > all RAID5/6 normal mode bugs with enough test cases covering them. Actually, turns out even the _first_ mount gets bad, even without writing a single data byte. So it's not related to our single chunks bug. > > Obviously, this problem is somewhere with RAID5 rather than this patch set, > > but the safety check can't be removed before that is fixed. > > Do we have *safety check* in original behavior? > > At least v4.11-rc1, btrfs still allows us to mount raid5/6 degraded. > So the patchset itself is behaving just as old one. Right. Thus, there's no regression. As it's a strict improvement over previous state (ie, fixes raid1 issues), Tested-by: Adam Borowski <kilobyte@xxxxxxxxxx> (if you don't mind spamming commits with too many tags). > I'm completely fine to add a new patch to prohibit raid5/6 degraded mount, > but that would be a different enhancement though. Yeah. I guess it's more in the "don't use RAID5, there be dragons" land. Thanks for these patches, they fix the #1 problem people have with RAID1. [Apologies for that "✔" crap on some lines, my exit code on prompt thingy is very paste-unfriendly; I keep forgetting it so often that I'd better get rid of it...] -- ⢀⣴⠾⠻⢶⣦⠀ Meow! ⣾⠁⢠⠒⠀⣿⡁ ⢿⡄⠘⠷⠚⠋⠀ Collisions shmolisions, let's see them find a collision or second ⠈⠳⣄⠀⠀⠀⠀ preimage for double rot13! -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
