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Hi, I am contemplating using a NVRAM card for OSD journals in place of SSD drives in our ceph cluster. Configuration:
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4 Ceph servers
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Each server has 24 OSDs (each OSD is a 1TB SAS drive)
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1 PCIe NVRAM card of 16GB capacity per ceph server
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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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