Hello Theodore,

On 21 Nov 2018, at 03:07, Theodore Y. Ts'o [off-list ref] wrote:

*) Drop support for nodelalloc, and make delayed allocation the
  default.  (This requires dropping data=journal mode, since
  data=journal mode does not co-exist with delalloc.)

The last was assuming that there really wasn't good use cases where
people would really want to use nodelalloc, aside from ext3
bug-for-bug compatibility, and hopefully since most people are using
ext4 these days, it becomes easier to make the case tha we don't need
to support ext3's unusual performance attributes.

Currently Lustre FS uses “nodelalloc” option at least because of this two reasons:

- OSD (layer that interact with EXT4 (LDISKFS backend) expect synchronous behaviour.

- delalloc optimise block allocation the way useless for Lustre FS, because data is striped across of OSTs. 
Lustre FS has its own optimisations. Its behaviour similar with data=journal journaling mode. “Journal” is stored on clients and OST recovery is like journal replay.

Best regards,
Artem Blagodarenko.