Hi,

>>What I saw after enabling RBD cache it is working as expected, means 
>>sequential write has better MBps than random write. can somebody explain this 
>>behaviour ?

This is because rbd_cache merge coalesced ios in bigger ios, so it's working 
only with sequential workload.

you'll do less ios but bigger ios to ceph, so less cpus,....


----- Mail original -----
De: "Sumit Gaur" <sumitkg...@gmail.com>
À: "Florent MONTHEL" <fmont...@flox-arts.net>
Cc: "ceph-users" <ceph-users@lists.ceph.com>
Envoyé: Lundi 2 Février 2015 03:54:36
Objet: Re: [ceph-users] ceph Performance random write is more then      
sequential

Hi All, 
What I saw after enabling RBD cache it is working as expected, means sequential 
write has better MBps than random write. can somebody explain this behaviour ? 
Is RBD cache setting must for ceph cluster to behave normally ? 

Thanks 
sumit 

On Mon, Feb 2, 2015 at 9:59 AM, Sumit Gaur < sumitkg...@gmail.com > wrote: 



Hi Florent, 
Cache tiering , No . 

** Our Architecture : 

vdbench/FIO inside VM <--> RBD without cache <-> Ceph Cluster (6 OSDs + 3 Mons) 


Thanks 
sumit 

[root@ceph-mon01 ~]# ceph -s 
cluster 47b3b559-f93c-4259-a6fb-97b00d87c55a 
health HEALTH_WARN clock skew detected on mon.ceph-mon02, mon.ceph-mon03 
monmap e1: 3 mons at {ceph-mon01= 
192.168.10.19:6789/0,ceph-mon02=192.168.10.20:6789/0,ceph-mon03=192.168.10.21:6789/0
 }, election epoch 14, quorum 0,1,2 ceph-mon01,ceph-mon02,ceph-mon03 
osdmap e603: 36 osds: 36 up, 36 in 
pgmap v40812: 5120 pgs, 2 pools, 179 GB data, 569 kobjects 
522 GB used, 9349 GB / 9872 GB avail 
5120 active+clean 


On Mon, Feb 2, 2015 at 12:21 AM, Florent MONTHEL < fmont...@flox-arts.net > 
wrote: 

BQ_BEGIN
Hi Sumit 

Do you have cache pool tiering activated ? 
Some feed-back regarding your architecture ? 
Thanks 

Sent from my iPad 

> On 1 févr. 2015, at 15:50, Sumit Gaur < sumitkg...@gmail.com > wrote: 
> 
> Hi 
> I have installed 6 node ceph cluster and to my surprise when I ran rados 
> bench I saw that random write has more performance number then sequential 
> write. This is opposite to normal disk write. Can some body let me know if I 
> am missing any ceph Architecture point here ? 
> _______________________________________________ 
> ceph-users mailing list 
> ceph-users@lists.ceph.com 
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com 





BQ_END



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