On 07/09/2014 05:57 AM, Xabier Elkano wrote:
Hi,
I was doing some tests in my cluster with fio tool, one fio instance
with 70 jobs, each job writing 1GB random with 4K block size. I did this
test with 3 variations:
1- Creating 70 images, 60GB each, in the pool. Using rbd kernel module,
format and mount each image as ext4. Each fio job writing in a separate
image/directory. (ioengine=libaio, queue_depth=4, direct=1)
IOPS: 6542
AVG LAT: 41ms
2- Creating 1 large image 4,2TB in the pool. Using rbd kernel module,
format and mount the image as ext4. Each fio job writing in a separate
file in the same directory. (ioengine=libaio, queue_depth=4,direct=1)
IOPS: 5899
AVG LAT: 47ms
3- Creating 1 large image 4,2TB in the pool. Use ioengine rbd in fio to
access the image through librados. (ioengine=rbd, queue_depth=4,direct=1)
IOPS: 2638
AVG LAT: 96ms
Do these results make sense? From Ceph perspective, It is better to have
many small images than a larger one? What is the best approach to
simulate the workload of 70 VMs?
I'm not sure the difference between the first two cases is enough to say
much yet. You may need to repeat the test a couple of times to ensure
that the difference is more than noise. having said that, if we are
seeing an effect, it would be interesting to know what the latency
distribution is like. is it consistently worse in the 2nd case or do we
see higher spikes at specific times?
In case 3, do you have multiple fio jobs going or just 1?
thanks in advance or any help,
Xabier
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