Hi Sridhar. Thanks for your reply:
We are testing migrations from a cluster running Pacific to Reef. In pacific we needed to tweak osd_mclock_max_capacity_iops_hdd to have decent performances of ou cluster.
It would be helpful to know the procedure you are employing for the migration.
For now we run some benchmarks on a fairly small dev/test cluster. It has been deployed using cephadm and updated with cephadm from Pacific to Reef. What we observed, is that with Pacific, tweaking osd_mclock_max_capacity_iops_hdd, we can go from arround 200MB/s of writes up to 600MB/s of writes, on balanced profile. But with Reef, changing osd_mclock_max_capacity_iops_hdd does not change a lot the performances of the cluster. (Or if it does, they are small enough so I did not see them). That been said, the performances of Reef "out of the box" are what we expect of our cluster (arround 600MB/s), while with Pacific we needed to tweak manually osd_mclock_max_capacity_iops_hdd to get the expected performances. So there is definitely a big improvement there. What made me think that this option was maybe not used anymore, during the deploy of Pacific, each OSD pushes its own osd_mclock_max_capacity_iops_hdd, but deploying Reef not. We did not see any values for the OSDs in the ceph config db. In conclusion, we could say, at least on our pre-update tests, that mClock seems to behave a lot better in Reef than in Pacific. Luis Domingues Proton AG On Monday, 8 January 2024 at 12:29, Sridhar Seshasayee <sseshasa@redhat.com> wrote:
Hi Luis,
We are testing migrations from a cluster running Pacific to Reef. In pacific we needed to tweak osd_mclock_max_capacity_iops_hdd to have decent performances of ou cluster.
It would be helpful to know the procedure you are employing for the migration.
But in reef it looks like changing the value of osd_mclock_max_capacity_iops_hdd does not impact cluster performances. Did osd_mclock_max_capacity_iops_hdd became useless?
"osd_mclock_max_capacity_iops_hdd" is still valid in Reef as long as it accurately represents the capability of the underlying OSD device for the intended workload.
Between Pacific and Reef many improvements to the mClock feature have been made. An important change relates to the automatic determination of cost per I/O which is now tied to the sequential and random IOPS capability of the underlying device of an OSD. As long as "osd_mclock_max_capacity_iops_hdd" and "osd_mclock_max_sequential_bandwidth_hdd" represent a fairly accurate capability of the backing OSD device, the performance should be along expected lines. Changing the "osd_mclock_max_capacity_iops_hdd" to a value that is beyond the capability of the device will obviously not yield any improvement.
If the above parameters are representative of the capability of the backing OSD device and you still see lower than expected performance, then it could be some other issue that needs looking into. -Sridhar _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io