https://ceph.io/en/news/blog/2015/ceph-activate-rbd-readhead/ https://www.oreilly.com/library/view/mastering-ceph/9781785888786/e0e9842f-6a86-4864-8b54-7f069aadf9d6.xhtml https://documentation.suse.com/ses/6/html/ses-all/tuning-ceph.html