On 2019/5/17 下午5:43, David Sterba wrote: > The list of profiles in btrfs_chunk_max_errors lists DUP as a profile > DUP able to tolerate 1 device missing. Though this profile is special > with 2 copies, it still needs the device, unlike the others. > > Looking at the history of changes, thre's no clear reason why DUP is > there, functions were refactored and blocks of code merged to one > helper. > > d20983b40e828 Btrfs: fix writing data into the seed filesystem > - factor code to a helper > > de11cc12df173 Btrfs: don't pre-allocate btrfs bio > - unrelated change, DUP still in the list with max errors 1 > > a236aed14ccb0 Btrfs: Deal with failed writes in mirrored configurations > - introduced the max errors, leaves DUP and RAID1 in the same group > > CC: Qu Wenruo <w...@suse.com> > Signed-off-by: David Sterba <dste...@suse.com
Reviewed-by: Qu Wenruo <w...@suse.com>
Just some extra hint for the tolerance of DUP profile.
In case of DUP, either all stripes are missing, or all stripes exist.
So no matter whether the tolerance is 0 or 1, it will always work.
But indeed, setting it to 0 is more accurate.
Thanks,
Qu
> ---
> fs/btrfs/volumes.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 1c2a6e4b39da..8508f6028c8d 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -5328,8 +5328,7 @@ static inline int btrfs_chunk_max_errors(struct
> map_lookup *map)
>
> if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
> BTRFS_BLOCK_GROUP_RAID10 |
> - BTRFS_BLOCK_GROUP_RAID5 |
> - BTRFS_BLOCK_GROUP_DUP)) {
> + BTRFS_BLOCK_GROUP_RAID5)) {
> max_errors = 1;
> } else if (map->type & BTRFS_BLOCK_GROUP_RAID6) {
> max_errors = 2;
>
signature.asc
Description: OpenPGP digital signature
