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
