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<< Ceph performance in general (without read_ahead_kb) will be lower specially in all flash as the requests will be serialized within a PG I meant to say Ceph sequential performance..Sorry for the spam.. From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx]
On Behalf Of Somnath Roy Not exactly, but, we are seeing some drop with 256K compare to 64K. This is with random reads though in Ubuntu. We had to bump up read_ahead_kb from default 128KB to 512KB to work around that. But, in RHEL we saw all sorts of issues with read_ahead_kb for small block random reads and I think it is already default to 4MB or so..If so, try to reduce it to 512KB and see.. Generally, for sequential reads, you need to play with read_ahead_kb to achieve better performance. Ceph performance in general (without read_ahead_kb) will be lower specially in all flash as the requests will
be serialized within a PG. Our test is with all flash though and take my comments with a grain of salt in case of ceph + HDD.. Thanks & Regards Somnath From: EP Komarla [mailto:Ep.Komarla@xxxxxxxxxxxxxxx]
Thanks Somnath. I am running with CentOS7.2. Have you seen this pattern before? - epk From: Somnath Roy [mailto:Somnath.Roy@xxxxxxxxxxx]
Which OS/kernel you are running with ? Try setting bigger read_ahead_kb for sequential runs. Thanks & Regards Somnath From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx]
On Behalf Of EP Komarla Hi, I am showing below fio results for Sequential Read on my Ceph cluster. I am trying to understand this pattern: - why there is a dip in the performance for block sizes 32k-256k? - is this an expected performance graph? - have you seen this kind of pattern before
My cluster details: Ceph: Hammer release Cluster: 6 nodes (dual Intel sockets) each with 20 OSDs and 4 SSDs (5 OSD journals on one SSD) Client network: 10Gbps Cluster network: 10Gbps FIO test:
- 2 Client servers - Sequential Read - Run time of 600 seconds - Filesize = 1TB - 10 rbd images per client - Queue depth=16 Any ideas on tuning this cluster? Where should I look first? Thanks, - epk
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