Hi Jesper, It could make sens only if: 1. the metadata the client's asking for was not already cached in RAM 2. the metadata pool was hosted on very low latency devices like NVMes 3. you could make sure that each client's metadata requests would be served from PGs for which the primary OSD is local to the MDS the client's talking to which in realy life is impossible to achieve as you cannot pin cephfs trees and their related metadata objects to specific PGs. Best regards, Frédéric. -- Cordialement, Frédéric Nass Direction du Numérique Sous-Direction Infrastructures et Services Université de Lorraine. Le 09/03/2021 à 16:03, Jesper Lykkegaard Karlsen a écrit :
Dear Ceph’ers
I am about to upgrade MDS nodes for Cephfs in the Ceph cluster (erasure code 8+3 ) I am administrating.
Since they will get plenty of memory and CPU cores, I was wondering if it would be a good idea to move metadata OSDs (NVMe's currently on OSD nodes together with cephfs_data ODS (HDD)) to the MDS nodes?
Configured as:
4 x MDS with each a metadata OSD and configured with 4 x replication
so each metadata OSD would have a complete copy of metadata.
I know MDS, stores al lot of metadata in RAM, but if metadata OSDs were on MDS nodes, would that not bring down latency?
Anyway, I am just asking for your opinion on this? Pros and cons or even better somebody who actually have tried this?
Best regards, Jesper
-------------------------- Jesper Lykkegaard Karlsen Scientific Computing Centre for Structural Biology Department of Molecular Biology and Genetics Aarhus University Gustav Wieds Vej 10 8000 Aarhus C
E-mail: jelka@mbg.au.dk<mailto:jelka@mbg.au.dk> Tlf: +45 50906203
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-- Cordialement, Frédéric Nass Direction du Numérique Sous-Direction Infrastructures et Services Université de Lorraine.