Re: cephfs vs rbd

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Buenos días, Jorge,

Muy interesante la prueba,
¿Dado que veo que trasteas mucho con ceph, me puedes responder a una duda? Como calcula Ceph el espacio disponible de disco, no termino de entender cómo es que, si tienes 3 servidores con 5 discos en cada uno de ellos, solo quedan efectivos un tercio del total de todos los discos, cuando tiene que mantener vivo 2 servidores, es más lógico que brinde un espacio de 2 tercios y se quede con 1 tercio para la replicación de datos


Un saludo


-----Mensaje original-----
De: Jorge Garcia <jgarcia@xxxxxxxxxxxx> 
Enviado el: viernes, 8 de octubre de 2021 21:21
Para: ceph-users@xxxxxxx
Asunto:  cephfs vs rbd

I was wondering about performance differences between cephfs and rbd, so I deviced this quick test. The results were pretty surprising to me.

The test: on a very idle machine, make 2 mounts. One is a cephfs mount, the other an rbd mount. In each directory, copy a humongous .tgz file
(1.5 TB) and try to untar the file into the directory. The untar on the cephfs directory took slightly over 2 hours, but on the rbd directory it took almost a whole day. I repeated the test 3 times and the results were similar each time. Is there something I'm missing? Is RBD that much slower than cephfs (or is cephfs that much faster than RBD)? Are there any tuning options I can try to improve RBD performance?

   # df -h | grep mnt
   10.1.1.150:/                          275T  1.5T  273T   1% /mnt/cephfs
   /dev/rbd0                              20T  1.5T   19T   8% /mnt/rbd

   bash-4.4$ pwd
   /mnt/cephfs/test
   bash-4.4$ date; time tar xf exceRptDB_v4_EXOGenomes.tgz; date
   Fri Jul  2 13:10:01 PDT 2021

   real    137m22.601s
   user    1m6.222s
   sys     35m57.697s
   Fri Jul  2 15:27:23 PDT 2021

   bash-4.4$ pwd
   /mnt/rbd/test
   bash-4.4$ date; time tar xf exceRptDB_v4_EXOGenomes.tgz; date
   Fri Jul  2 15:38:28 PDT 2021

   real    1422m42.236s
   user    1m34.198s
   sys     38m48.761s
   Sat Jul  3 15:21:10 PDT 2021



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