On 2019-11-08 10:24 a.m., Nate Eldredge wrote:
> On Fri, 8 Nov 2019, Qu Wenruo wrote:
> 
>> In fact, you can just go nodatacow.
>> Furthermore, nodatacow attr can be applied to a directory so that any
>> newer file will just inherit the nodatacow attr.
>>
>> In that case, any overwrite will not be COWed (as long as there is no
>> snapshot for it), thus no space wasted.
> 
> Aha, I didn't know about that feature.  Thanks, that is exactly what I
> want.
> 


I would advise caution with this approach.. with nodatacow you give up
all of the features that would make you want to use BTRFS in the first
place.  (No Checksum verification, for example.)

And if using in conjunction with BTRFS Raid, BTRFS behavior, is,, in
terms of RAID, outright psychotic.  In case of unclean shutdown while
data was being written, the RAID copies will be inconsistent, and BTRFS
will never synchronize them, (short of a full re-balance.).. What data
gets read will just randomnly depend on what device BTRFS is reading from.

If you would rather forgo the benefits of BTRFS for better performance
or fragmentation issues, why not carve out an XFS / EXT4 partition?