[ceph-users] how to improve performance

ulembke at polarzone.de ulembke at polarzone.de
Mon Nov 20 08:30:53 PST 2017


Hi,
not flushing the ceph-journal!

I speak about the caching from linux.
If you run free, you can see how much is cached:
like
# free
               total        used        free      shared  buff/cache   
available
Mem:       41189692    16665960     4795700      124780    19728032    
28247464

To free the cache (normly not done in productional systems):
sync; echo 3 > /proc/sys/vm/drop_caches

look after that with free and run your bench (only read) again.


Udo


Am 2017-11-20 13:06, schrieb Rudi Ahlers:
> Hi,
> 
> So are you saying this isn't true speed?
> 
> Do I just flush the journal and test again? i.e. ceph-osd -i osd.0
> --flush-journal && ceph-osd -i osd.2 --flush-journal && ceph-osd -i 
> osd.3
> --flush-journal etc, etc?
> 
> On Mon, Nov 20, 2017 at 2:02 PM, <ulembke at polarzone.de> wrote:
> 
>> Hi Rudi,
>> 
>> Am 2017-11-20 11:58, schrieb Rudi Ahlers:
>> 
>>> ...
>>> 
>>> Some more stats:
>>> 
>>> root at virt2:~# rados bench -p Data 10 seq
>>> hints = 1
>>>   sec Cur ops   started  finished  avg MB/s  cur MB/s last lat(s)  
>>> avg
>>> lat(s)
>>>     0       0         0         0         0         0           -
>>>  0
>>>     1      16       402       386   1543.69      1544  0.00182802
>>>  0.0395421
>>>     2      16       773       757   1513.71      1484  0.00243911
>>>  0.0409455
>>> 
>>> this values are due cached osd-data on your osd-nodes.
>> 
>> If you flush your cache (on all osd-nodes), your reads will be much 
>> worse,
>> because they came from the HDDs.
>> 
>> 
>> Udo
>> 


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