Rather than a cache tier, I would put an NVMe device in each OSD box for Bluestore's DB and WAL. This will significantly improve small IOs. 14*16 HDDs / 11 chunks = 20 HDD's worth of write IOPs. If you expect these files to be written sequentially, this is probably ok. Mons and mgr on OSD nodes should be ok as far as I know (we are doing it). However, if you use CephFS, you will want the fastest CPUs you can get for the MDS, as it only scales to 2-3 cores in our tests. I would avoid the complexity of CephFS if you do not need POSIX semantics. On Tue, Dec 3, 2019 at 3:07 PM Fabien Sirjean <fsirjean@eddie.fdn.fr> wrote:
Hi Ceph users !
After years of using Ceph, we plan to build soon a new cluster bigger than what we've done in the past. As the project is still in reflection, I'd like to have your thoughts on our planned design : any feedback is welcome :)
## Requirements
* ~1 PB usable space for file storage, extensible in the future * The files are mostly "hot" data, no cold storage * Purpose : storage for big files being essentially used on windows workstations (10G access) * Performance is better :)
## Global design
* 8+3 Erasure Coded pool * ZFS on RBD, exposed via samba shares (cluster with failover)
## Hardware
* 1 rack (multi-site would be better, of course...)
* OSD nodes : 14 x supermicro servers * 24 usable bays in 2U rackspace * 16 x 10 TB nearline SAS HDD (8 bays for future needs) * 2 x Xeon Silver 4212 (12C/24T) * 128 GB RAM * 4 x 40G QSFP+
* Networking : 2 x Cisco N3K 3132Q or 3164Q * 2 x 40G per server for ceph network (LACP/VPC for HA) * 2 x 40G per server for public network (LACP/VPC for HA) * QSFP+ DAC cables
## Sizing
If we've done the maths well, we expect to have :
* 2.24 PB of raw storage, extensible to 3.36 PB by adding HDD * 1.63 PB expected usable space with 8+3 EC, extensible to 2.44 PB * ~1 PB of usable space if we want to keep the OSD use under 66% to allow loosing nodes without problem, extensible to 1.6 PB (same condition)
## Reflections
* We're used to run mons and mgrs daemons on a few of our OSD nodes, without any issue so far : is this a bad idea for a big cluster ?
* We thought using cache tiering on an SSD pool, but a large part of the PB is used on a daily basis, so we expect the cache to be not so effective and really expensive ?
* Could a 2x10G network be enough ?
* ZFS on Ceph ? Any thoughts ?
* What about CephFS ? We'd like to use RBD diff for backups but it looks impossible to use snapshot diff with Cephfs ?
Thanks for reading, and sharing your experiences !
F.
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