On 10/15/19 1:29 PM, Vitaliy Filippov wrote:
Wow, does it really work?
And why is it not supported by RBD?
Can you show us the latency graphs before and after and tell the I/O pattern to which the latency applies? Previous common knowledge was that RDMA almost doesn't affect latency with Ceph, because most of the latency is in Ceph itself.
This is still the case. RDMA might shave a bit off the network latency, but the code/CPU latency is still the highest in Ceph. There is no real benefit in using RDMA over Ethernet+IP as that latency is already very low with modern chips and switches. Wido
Hello!
Mon, Oct 14, 2019 at 07:28:07AM -0000, gabryel.mason-williams wrote:
Hello,
I was wondering what user experience was with using Ceph over RDMA? - How you set it up?
We had used RoCE Lag with Mellanox ConnectX-4 Lx.
- Documentation used to set it up?
Generally, Mellanox community docs and Ceph docs: https://community.mellanox.com/s/article/bring-up-ceph-rdma---developer-s-gu...
- Known issues when using it?
Ceph's distribution does not include Systemd units with LimitMEMLOCK=infinity setting. Also it was needed to start Ceph as root to workaround some limits. Ceph rbd clients, so as mgr daemons, do not suport rdma, so it was needed to set ms_cluster_type = async+rdma ms_type = async+rdma ms_public_type = async+posix [mgr] ms_type = async+posix
And we needed to disable any Jumbo Frames support in order to work with RDMA.
- If you still use it?
As I can see on my graphs, it is latency drop with Nautilus+RDMA. As for now, cluster is up and running for 2 weeks without any issues and with our production load (rbd, radosgw, cephfs). _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io