On Fri, Dec 13, 2019 at 11:21:07AM -0500, Josef Bacik wrote:
On 12/12/19 11:08 PM, Naohiro Aota wrote:
HMZONED mode cannot be used together with the RAID5/6 profile for now.
Introduce the function btrfs_check_hmzoned_mode() to check this. This
function will also check if HMZONED flag is enabled on the file system and
if the file system consists of zoned devices with equal zone size.
Additionally, as updates to the space cache are in-place, the space cache
cannot be located over sequential zones and there is no guarantees that the
device will have enough conventional zones to store this cache. Resolve
this problem by completely disabling the space cache. This does not
introduce any problems in HMZONED mode: all the free space is located after
the allocation pointer and no free space is located before the pointer.
There is no need to have such cache.
For the same reason, NODATACOW is also disabled.
Also INODE_MAP_CACHE is also disabled to avoid preallocation in the
INODE_MAP_CACHE inode.
In summary, HMZONED will disable:
| Disabled features | Reason |
|-------------------+-----------------------------------------------------|
| RAID5/6 | 1) Non-full stripe write cause overwriting of |
| | parity block |
| | 2) Rebuilding on high capacity volume (usually with |
| | SMR) can lead to higher failure rate |
|-------------------+-----------------------------------------------------|
| space_cache (v1) | In-place updating |
| NODATACOW | In-place updating |
|-------------------+-----------------------------------------------------|
| fallocate | Reserved extent will be a write hole |
| INODE_MAP_CACHE | Need pre-allocation. (and will be deprecated?) |
|-------------------+-----------------------------------------------------|
| MIXED_BG | Allocated metadata region will be write holes for |
| | data writes |
| async checksum | Not to mix up bios by multiple workers |
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
I assume the progs will be updated to account for these limitations as well?
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Thanks,
Josef
Oops, while it's errored out from mkfs.btrfs, I forgot to add early
check for RAID56 and MIXED_BG. I'll add the checks in the next series.
