Hi,
I am contemplating using a NVRAM card for OSD journals in place of SSD drives
in our ceph cluster.
Configuration:
* 4 Ceph servers
* Each server has 24 OSDs (each OSD is a 1TB SAS drive)
* 1 PCIe NVRAM card of 16GB capacity per ceph server
* Both Client & cluster network is 10Gbps
As per ceph documents:
The expected throughput number should include the expected disk throughput
(i.e., sustained data transfer rate), and network throughput. For example, a
7200 RPM disk will likely have approximately 100 MB/s. Taking the min() of the
disk and network throughput should provide a reasonable expected throughput.
Some users just start off with a 10GB journal size. For example:
osd journal size = 10000
Given that I have a single 16GB card per server that has to be carved among all
24OSDs, I will have to configure each OSD journal to be much smaller around
600MB, i.e., 16GB/24 drives. This value is much smaller than 10GB/OSD journal
that is generally used. So, I am wondering if this configuration and journal
size is valid. Is there a performance benefit of having a journal that is this
small? Also, do I have to reduce the default "filestore maxsync interval" from
5 seconds to a smaller value say 2 seconds to match the smaller journal size?
Have people used NVRAM cards in the Ceph clusters as journals? What is their
experience?
Any thoughts?
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