[pve-devel] ceph firefly in pve repos

[Stefan Priebe - Profihost AG]

Am 09.09.2014 um 09:40 schrieb Dietmar Maurer:
> The interesting thing is that write speed degrades if I do a long run (15 minutes):
> 
> # rados bench -p test3 900 write
>      0       0         0         0         0         0         -         0
>      1      16       184       168   671.851       672  0.061917 0.0903528
>      2      16       377       361   721.883       772  0.058924 0.0869117
>      3      16       575       559   745.227       792  0.107722 0.0844572
>  ...
> 900      15     51501     51486   228.795       232  0.280925  0.279647
> Total time run:         900.846099
> Total writes made:      51501
> Write size:             4194304
> Bandwidth (MB/sec):     228.678 
> 
> Stddev Bandwidth:       83.0067
> Max bandwidth (MB/sec): 632
> Min bandwidth (MB/sec): 0
> Average Latency:        0.279843
> Stddev Latency:         0.277617
> Max latency:            3.81218
> Min latency:            0.034482
> 
> I guess this is what Stefan is talking about?

Yes you can also verify this via fio.

fio --filename=$DISK --direct=1 --rw=write --bs=4M --numjobs=2
--group_reporting --invalidate=0 --name=abc

Just run this in an endless loop for several days (min 24h). Good SSDs
can keep up 240MB/s or up to 360MB/s.

The crucial ones go down to 80MB/s or even 40MB/s with massive latencies.

Stefan