>   iops        : min=    2, max=   40, avg=21.13, stdev= 6.10, samples=929
>   iops        : min=    2, max=   42, avg=21.52, stdev= 6.56, samples=926

That looks horrible. We also have a few SATA HDDs in Dell servers and they do 
about 100-150 IOP/s read or write. Originally, I was also a bit afraid that 
these disks would drag performance down, but they are on par with the NL-SAS 
drives.

For ceph we use the cheapest Dell disk controller one can get (Dell HBA330 Mini 
(Embedded)) and it works perfectly. All ceph-disks are configured non-raid, 
which is equivalent to JBOD mode or pass-through. These controllers have no 
cache options, if your do, disable all of them. Mode should be write-through.

For your disk type I saw "volatile write cache available = yes" on "the 
internet". This looks a bit odd, but maybe these HDDs do have some volatile 
cache. Try to disable it with smartctl and do the benchmark again.

Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
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