Hi Christian,
Thanks for your reply.
What SSD model (be precise)?
Samsung 480GB PM863 SSD
Only one SSD?
Yes. With a 5GB partition based journal for each osd.
During the 0 MB/sec, there is NO increased cpu usage: it is usually
around 15 - 20% for the four ceph-osd processes.
Watch your node(s) with atop or iostat.
Ok, I will do.
Do we have an issue..? And if yes: Anyone with a suggestions where to
look at?
You will find that either your journal SSD is overwhelmed and a single
SSD peaking around 500MB/s wouldn't be that surprising.
Or that your HDDs can't scribble away at more than the speed above, the
more likely reason.
Even a combination of both.
Ceph needs to flush data to the OSDs eventually (and that is usually more
or less immediately with default parameters), so for a sustained,
sequential write test you're looking at the speed of your HDDs.
And that will be spiky of sorts, due to FS journals, seeks for other
writes (replicas), etc.
But would we expect the MB/sec to drop to ZERO, during journal-to-osd
flushes?
Thanks for the quick feedback, and I'll dive into atop and iostat next.
Regards,
MJ
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