Hello,

I am deploying a new Nautilus cluster and I would like to know what would be 
the best OSD's scenario config in this case :

10x 6TB Disk OSDs (data)
 2x 480G SSD previously used for journal and can be used for WAL and/or DB

Is it better to put all WAL on one SSD and all DBs on the other one? Or put WAL 
and DB of the first 5 OSDs on the first SSD and the 5 others on
the second one.

A more general question, what is the impact on an OSD if we lose the WAL? The 
DB? Both?

I plan to use EC 7+5 on 12 servers and I am OK if I lose one server 
temporarily. I have spare servers and I can easily add another one in this
cluster.

To deploy this cluster, I use ceph-ansible (stable-4.0). I am not sure how to 
configure the playbook to use SSD and disks with LVM.

https://github.com/ceph/ceph-ansible/blob/master/docs/source/osds/scenarios.rst

Is this good?

osd_objectstore: bluestore
lvm_volumes:
  - data: data-lv1
    data_vg: data-vg1
    db: db-lv1
    db_vg: db-vg1
    wal: wal-lv1
    wal_vg: wal-vg1
  - data: data-lv2
    data_vg: data-vg2
    db: db-lv2
    db_vg: db-vg2
    wal: wal-lv2
    wal_vg: wal-vg2


Is it possible to let the playbook configure LVM for each disk in a mixed case? 
It looks like I must configure LVM before running the playbook
but I am not sure if I missed something.

Is wal_vg and db_vg can be identical (on VG per SSD shared with multiple OSDs)?

Thanks for your help.

Best regards,

-- 
Yoann Moulin
EPFL IC-IT
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