On Mon, Oct 08, 2018 at 04:10:55PM +0000, Hugo Mills wrote: > On Mon, Oct 08, 2018 at 03:49:53PM +0200, Pierre Couderc wrote: > > I ma trying to make a "RAID1" with /dev/sda2 ans /dev/sdb (or similar). > > > > But I have stranges status or errors about "missing devices" and I > > do not understand the current situation : [...] > Note that, since the main FS is missing a device, it will probably > need to be mounted in degraded mode (-o degraded), and that on kernels > earlier than (IIRC) 4.14, this can only be done *once* without the FS > becoming more or less permanently read-only. On recent kernels, it > _should_ be OK. > > *WARNING ENDS*
I think this was the patch that addressed this?: https://www.spinics.net/lists/linux-btrfs/msg47283.html https://patchwork.kernel.org/patch/7226931/ In my notes it wasn't present in <= 4.14.15, but my notes might be wrong. Does this patch resolve the one-shot -o degraded, reboot, forever read-only behaviour, or is something else required? When was it merged? Has it been or will it be backported to 4.14.x? I'm guessing 4.9.x is too far back, but it would be really nice to see it there too :-) Also, will this issue be resolved for linux-4.19? If so I'd like to update the Debian btrfs wiki with this good news :-) Finally, is the following a valid workaround for users who don't have access to a kernel containing this fix: 1. Make a raid1 profile volume (both data and metadata) with >= 3 disks. 2. Lose one disk. 3. Allocator continues to write raid1 chunks instead of single, because it is still possible to write one chunk to two disks. 4. Thus reboot twice -> forever read-only averted? Kind regards, Nicholas P.S. Please let me know if you'd prefer for me to shift this documentation effort to btrfs.wiki.kernel.org.
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