Re: MDS cache tunning

[Andres Rojas Guerrero <a.rojas@xxxxxxx>]

Thanks for the answer. Yes, during these last weeks I have had memory 
consumption problems in the MDS nodes that led, at least it seemed to 
me, to performance problems in CephFS. I have been varying, for example:

mds_cache_memory_limit
mds_min_caps_per_client
mds_health_cache_threshold
mds_max_caps_per_client
mds_cache_reservation

But without much knowledge and with a trial and error procedure, i.e. 
observing how CephFS behaved when changing one of the parameters. 
Although I have achieved improvement the procedure does not convince me 
at all and that's why I was asking if there was something  more reliable ...




El 26/5/21 a las 12:15, Dan van der Ster escribió:
> Hi,
>
> The mds_cache_memory_limit should be set to something relative to the
> RAM size of the MDS -- maybe 50% is a good rule of thumb, because
> there are a few cases where the RSS can exceed this limit. Your
> experience will help guide what size you need (metadata pool IO
> activity will be really high if the MDS cache is too small)
>
> Otherwise, in recent releases of N/O/P the defaults for those settings
> you mentioned are quite good [1]; I would be surprised if they need
> further tuning for 99% of users.
> Is there any reason you want to start adjusting these params?
>
> Best Regards,
>
> Dan
>
> [1] https://github.com/ceph/ceph/pull/38574
>
> On Wed, May 26, 2021 at 11:58 AM Andres Rojas Guerrero <a.rojas@xxxxxxx> wrote:
> > Hi all, I have observed that the MDS Cache Configuration has 18 parameters:
> >
> > mds_cache_memory_limit
> > mds_cache_reservation
> > mds_health_cache_threshold
> > mds_cache_trim_threshold
> > mds_cache_trim_decay_rate
> > mds_recall_max_caps
> > mds_recall_max_decay_threshold
> > mds_recall_max_decay_rate
> > mds_recall_global_max_decay_threshold
> > mds_recall_warning_threshold
> > mds_recall_warning_decay_rate
> > mds_session_cap_acquisition_throttle
> > mds_session_cap_acquisition_decay_rate
> > mds_session_max_caps_throttle_ratio
> > mds_cap_acquisition_throttle_retry_request_timeout
> > mds_session_cache_liveness_magnitude
> > mds_session_cache_liveness_decay_rate
> > mds_max_caps_per_client
> >
> >
> >
> > I find the Ceph documentation in this section a bit cryptic and I have
> > tried to find some resources that talk about how to tune these
> > parameters, but without success.
> >
> > Does anyone have experience in adjusting these parameters according to
> > the characteristics of the Ceph cluster itself, the hardware and the use
> > of MDS?
> >
> > Regards!
> > --
> > *******************************************************
> > Andrés Rojas Guerrero
> > Unidad Sistemas Linux
> > Area Arquitectura Tecnológica
> > Secretaría General Adjunta de Informática
> > Consejo Superior de Investigaciones Científicas (CSIC)
> > Pinar 19
> > 28006 - Madrid
> > Tel: +34 915680059 -- Ext. 990059
> > email: a.rojas@xxxxxxx
> > ID comunicate.csic.es: @50852720l:matrix.csic.es
> > *******************************************************
> > _______________________________________________
> > ceph-users mailing list -- ceph-users@xxxxxxx
> > To unsubscribe send an email to ceph-users-leave@xxxxxxx

--
*******************************************************
Andrés Rojas Guerrero
Unidad Sistemas Linux
Area Arquitectura Tecnológica
Secretaría General Adjunta de Informática
Consejo Superior de Investigaciones Científicas (CSIC)
Pinar 19
28006 - Madrid
Tel: +34 915680059 -- Ext. 990059
email: a.rojas@xxxxxxx
ID comunicate.csic.es: @50852720l:matrix.csic.es
*******************************************************

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