On 09/17/2013 03:30 PM, Somnath Roy wrote:
Hi,
I am running Ceph on a 3 node cluster and each of my server node is running 10
OSDs, one for each disk. I have one admin node and all the nodes are connected
with 2 X 10G network. One network is for cluster and other one configured as
public network.
Here is the status of my cluster.
~/fio_test# ceph -s
cluster b2e0b4db-6342-490e-9c28-0aadf0188023
health HEALTH_WARN clock skew detected on mon. <server-name-2>, mon.
<server-name-3>
monmap e1: 3 mons at {<server-name-1>=xxx.xxx.xxx.xxx:6789/0,
<server-name-2>=xxx.xxx.xxx.xxx:6789/0, <server-name-3>=xxx.xxx.xxx.xxx:6789/0}, election epoch 64,
quorum 0,1,2 <server-name-1>,<server-name-2>,<server-name-3>
osdmap e391: 30 osds: 30 up, 30 in
pgmap v5202: 30912 pgs: 30912 active+clean; 8494 MB data, 27912 MB used,
11145 GB / 11172 GB avail
mdsmap e1: 0/0/1 up
I started with rados bench command to benchmark the read performance of this
Cluster on a large pool (~10K PGs) and found that each rados client has a
limitation. Each client can only drive up to a certain mark. Each server node
cpu utilization shows it is around 85-90% idle and the admin node (from where
rados client is running) is around ~80-85% idle. I am trying with 4K object
size.
Note that rados bench with 4k objects is different from rbd with
4k-sized I/Os - rados bench sends each request to a new object,
while rbd objects are 4M by default.
Now, I started running more clients on the admin node and the performance is
scaling till it hits the client cpu limit. Server still has the cpu of 30-35%
idle. With small object size I must say that the ceph per osd cpu utilization
is not promising!
After this, I started testing the rados block interface with kernel rbd module
from my admin node.
I have created 8 images mapped on the pool having around 10K PGs and I am not
able to scale up the performance by running fio (either by creating a software
raid or running on individual /dev/rbd* instances). For example, running
multiple fio instances (one in /dev/rbd1 and the other in /dev/rbd2) the
performance I am getting is half of what I am getting if running one instance.
Here is my fio job script.
[random-reads]
ioengine=libaio
iodepth=32
filename=/dev/rbd1
rw=randread
bs=4k
direct=1
size=2G
numjobs=64
Let me know if I am following the proper procedure or not.
But, If my understanding is correct, kernel rbd module is acting as a client to
the cluster and in one admin node I can run only one of such kernel instance.
If so, I am then limited to the client bottleneck that I stated earlier. The
cpu utilization of the server side is around 85-90% idle, so, it is clear that
client is not driving.
My question is, is there any way to hit the cluster with more client from a
single box while testing the rbd module ?
You can run multiple librbd instances easily (for example with
multiple runs of the rbd bench-write command).
The kernel rbd driver uses the same rados client instance for multiple
block devices by default. There's an option (noshare) to use a new
rados client instance for a newly mapped device, but it's not exposed
by the rbd cli. You need to use the sysfs interface that 'rbd map' uses
instead.
Once you've used rbd map once on a machine, the kernel will already
have the auth key stored, and you can use:
echo '1.2.3.4:6789 name=admin,key=client.admin,noshare poolname
imagename' > /sys/bus/rbd/add
Where 1.2.3.4:6789 is the address of a monitor, and you're connecting
as client.admin.
You can use 'rbd unmap' as usual.
Josh
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