Hi,

The results look strange to me...

To begin with, it's strange that read and write performance differs. But
the thing is that a lot (if not most) large Seagate EXOS drives have
internal SSD cache (~8 GB of it). I suspect that new EXOS also does and
I'm not sure if Toshiba has it. It could explain the write performance
difference in your test.

Try to disable Seagates' write cache with sdparm --set WCE=0 /dev/sdX
and see how the performance changes. If there is an SSD cache you'll
probably see an increase in iops. Due to the nature of Bluestore and at
least with an external block.db on SSD the difference is like ~230 iops
vs ~1200 iops with iodepth=1. This is the result for ST8000NM0055.

Also it's strange that read performance is almost the same. Can you
benchmark the drive with fio alone, without Ceph?

> Hi,
>
> we ran some benchmarks with a few samples of Seagate's new HDDs that
> some of you might find interesting:
>
> Blog post:
>
> https://croit.io/2020/01/06/2020-01-06-benchmark-mach2
>
> GitHub repo with scripts and raw data:
> https://github.com/croit/benchmarks/tree/master/mach2-disks
>
> Tl;dr: way faster for writes, somewhat faster for reads in some
> scenarios
>
> Paul
>
> --
> Paul Emmerich
>
> Looking for help with your Ceph cluster? Contact us at
> https://croit.io
>
> Looking for Ceph training? We have some free spots available
> https://croit.io/training/4-days-ceph-in-depth-training
>
> croit GmbH
> Freseniusstr. 31h
> 81247 München
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> Tel: +49 89 1896585 90
>
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