[ceph-users] DB sizing for lots of large files

Hi, Sorry to bother you all. It’s a home server setup. Three nodes (ODROID-H2+ with 32GB RAM and dual 2.5Gbit NICs), two 14TB 7200rpm SATA drives and an Optane 118GB NVMe in each node (OS boots from eMMC). Only CephFS, I'm anticipating having 50-200K files when the 50TB (4+2 EC) is full. I'm trying to address the issue of really big OSD's, not my words, a Redditor: "When you write an object to a drive with collocated db and raw space, the disk has to read/write to both sections before acking a write. That's a lot to ask a 7200 disk to handle gracefully. I believe Red Hat only supports up to 8TB because of performance concerns with larger disks. I may be wrong, but once you are shuffling through 6-10TB of data I'd think those disks are gonna be bogged down in seek time." So I want to have my two DB's on the Optane to avoid the above, am I making sense? OK, so large files have lower metadata overhead than small files. This is for a media library this probably means super low overhead, one guy I spoke to had similar setup and for 48TB used he had a 2.6GB DB? Is there a rough CephFS calculation (each file uses x bytes of metadata), I think I should be safe with 30GB, now I read I should double that (you should allocate twice the size of the biggest layer to allow for compaction) but I only have 118GB and two OSDs so I will have to go for 59GB (or whatever will fit)? I'm thinking that I might not even use 3GB but to be safe I’ll make it 30GB, lets say it settles at 5GB, when compaction comes that means I will only need 20GB and therefore no spillover? I realise that if the Optane dies both OSD's go with it, do I have to configure anything special there (CRUSH would just handle it)? Being that this a home deployment will Ceph be OK with an occasional power outage, I mean if a bluray mkv gets corrupted ripping it again is an easy fix, also I will backup the clusters data once a month? Below are the commands I got from the website: Create the volume groups: $ vgcreate ceph-block-0 /dev/sda $ vgcreate ceph-block-1 /dev/sdb Create the logical volumes: $ lvcreate -l 100%FREE -n block-0 ceph-block-0 $ lvcreate -l 100%FREE -n block-1 ceph-block-1 Create db logical volumes (118GB Optane) $ vgcreate ceph-db-0 /dev/sdc $ lvcreate -L 59GB -n db-0 ceph-db-0 $ lvcreate -L 59GB -n db-1 ceph-db-0 Create the OSDs $ ceph-volume lvm create --bluestore --data ceph-block-0/block-0 --block.db ceph-db-0/db-0 $ ceph-volume lvm create --bluestore --data ceph-block-1/block-1 --block.db ceph-db-0/db-1 Thanks. Richard