Re: [PATCH v2 0/6] Chunk level degradable check

[Dmitrii Tcvetkov <demfloro@demfloro.ru>]

On Mon, 6 Mar 2017 16:58:49 +0800
Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:

> Btrfs currently uses num_tolerated_disk_barrier_failures to do global
> check for tolerated missing device.
> 
> Although the one-size-fit-all solution is quite safe, it's too strict
> if data and metadata has different duplication level.
> 
> For example, if one use Single data and RAID1 metadata for 2 disks, it
> means any missing device will make the fs unable to be degraded
> mounted.
> 
> But in fact, some times all single chunks may be in the existing
> device and in that case, we should allow it to be rw degraded mounted.
> 
> Such case can be easily reproduced using the following script:
>  # mkfs.btrfs -f -m raid1 -d sing /dev/sdb /dev/sdc
>  # wipefs -f /dev/sdc
>  # mount /dev/sdb -o degraded,rw
> 
> If using btrfs-debug-tree to check /dev/sdb, one should find that the
> data chunk is only in sdb, so in fact it should allow degraded mount.
> 
> This patchset will introduce a new per-chunk degradable check for
> btrfs, allow above case to succeed, and it's quite small anyway.
> 
> And enhance kernel error message for missing device, at least kernel
> can know what's making mount failed, other than meaningless
> "failed to read system chunk/chunk tree -5".

Hello,

Tested the patchset for raid1 and raid10. Successfully allows
degraded mount with single chunks on the filesystems without one drive.

Feel free to add Tested-By: Dmitrii Tcvetkov <demfloro@demfloro.ru>