Hi - in my home , I have been running cephfs for a few years, and have 
reasonably good performance, however since exposing cephfs via SMB has been hit 
and miss.    So I thought I could carve out space for a RBD device to share 
from a windows machine


My set up:

CEPH 18.2.2  deployed using ceph adm

4 servers running RHEL9  on AMD 5600g  CPUs
64 Gb Each
10Gbe NICs
4x4Tb Hdd
1 2Tb NVME for DB/WAL
rbd pool is set to auto  PG - its currently at 256

I have tested the NIC connection between the servers and my PC, an each point 
to point works well at the 10Gbe speeds

Now the problem

I created a 8Tb RBD using

rbd create winshare -size 8T -pool rbd
rbd map winshare

I prepped the drive, formatted it, and the drive appears cleanly as an 8 Tb 
drive.

When I used fio on the drive/volume, speeds were good around 150-200 Mb/s.

Then I started trying to populate the drive from a few different sources, and 
performance took a nose dive.  - Write speeds are about 6-10 Mb/s,  and windows 
task manager shows  average response time  anywhere from 500ms to 30 seconds. - 
mainly around 4 seconds.


I don't see any obvious bottlenecks - cpu on the servers are about 5-10%, 
memory is good,   Network is showing under 1 Gb/s  on all servers.


I am wondering if I needed to use different parameters for creating the volume? 
 Or is there a practical limit to the volume size I exceeded?

Thanks,

Rob

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