[ceph-users] osd bench with or without a separate WAL device deployed

Hi all, I am wondering if there is any performance comparison done on osd bench with and without a separate WAL device deployed given that there is always a separate db device deployed on SSD in both cases. The reason I am asking this question is that we have two clusters and osds in one have separate db and WAL device deployed on SSD but osds in another only have a separate db device deployed. And we found 4KB osd bench (i.e. ceph tell osd.X bench 12288000 4096) for the ones having a separate WAL device was two times of the ones without a separate WAL device. Is the performance difference caused by the separate WAL device? Thanks, Ning