Hi,
We did a simple throughput test on Ceph with 2 OSD nodes configured
with one replica policy. For each OSD node, the throughput measured by
'dd' run locally is 117MB/s. Therefore, in theory, the two OSDs could
provide 200+MB/s throughput. However, using 'iozone' from clients we
only get a peak throughput at around 40MB/s. Is that because a write
will incur 2 replica * 2 journal write? That is, writing into journal
and replica doubled the traffic, respectively, which results in a total
4x write amplification. Is that true, or our understanding is wrong,
and some performance tuning hint?
Cheers,
Li Wang
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