While setting up my Ceph cluster on a set of Dell R710s, one with 60 disks attached to it, I found that I needed to raise fs.aio-max-nr to around 1,000,000. SELinux also needed to be disabled. Once that was done the normal cephadm osd install worked great, even with 60 disks. 

$ cat /etc/sysctl.d/99-osd.conf

# For OSDs