Chapter 7. Benchmarking Performance
The purpose of this section is to give Ceph administrators a basic understanding of Ceph’s native benchmarking tools. These tools will provide some insight into how the Ceph storage cluster is performing. This is not the definitive guide to Ceph performance benchmarking, nor is it a guide on how to tune Ceph accordingly.
7.1. Performance Baseline
The OSD (including the journal) disks and the network throughput should each have a performance baseline to compare against. You can identify potential tuning opportunities by comparing the baseline performance data with the data from Ceph’s native tools. Red Hat Enterprise Linux has many built-in tools, along with a plethora of open source community tools, available to help accomplish these tasks. For more details about some of the available tools, see this Knowledgebase article.
7.2. Storage Cluster
Ceph includes the rados bench command to do performance benchmarking on a RADOS storage cluster. The command will execute a write test and two types of read tests. The --no-cleanup option is important to use when testing both read and write performance. By default the rados bench command will delete the objects it has written to the storage pool. Leaving behind these objects allows the two read tests to measure sequential and random read performance.
Before running these performance tests, drop all the file system caches by running the following:
# echo 3 | sudo tee /proc/sys/vm/drop_caches && sudo sync
Create a new storage pool:
# ceph osd pool create testbench 100 100
Execute a write test for 10 seconds to the newly created storage pool:
# rados bench -p testbench 10 write --no-cleanup
Example Output
Maintaining 16 concurrent writes of 4194304 bytes for up to 10 seconds or 0 objects Object prefix: benchmark_data_cephn1.home.network_10510 sec Cur ops started finished avg MB/s cur MB/s last lat avg lat 0 0 0 0 0 0 - 0 1 16 16 0 0 0 - 0 2 16 16 0 0 0 - 0 3 16 16 0 0 0 - 0 4 16 17 1 0.998879 1 3.19824 3.19824 5 16 18 2 1.59849 4 4.56163 3.87993 6 16 18 2 1.33222 0 - 3.87993 7 16 19 3 1.71239 2 6.90712 4.889 8 16 25 9 4.49551 24 7.75362 6.71216 9 16 25 9 3.99636 0 - 6.71216 10 16 27 11 4.39632 4 9.65085 7.18999 11 16 27 11 3.99685 0 - 7.18999 12 16 27 11 3.66397 0 - 7.18999 13 16 28 12 3.68975 1.33333 12.8124 7.65853 14 16 28 12 3.42617 0 - 7.65853 15 16 28 12 3.19785 0 - 7.65853 16 11 28 17 4.24726 6.66667 12.5302 9.27548 17 11 28 17 3.99751 0 - 9.27548 18 11 28 17 3.77546 0 - 9.27548 19 11 28 17 3.57683 0 - 9.27548 Total time run: 19.505620 Total writes made: 28 Write size: 4194304 Bandwidth (MB/sec): 5.742 Stddev Bandwidth: 5.4617 Max bandwidth (MB/sec): 24 Min bandwidth (MB/sec): 0 Average Latency: 10.4064 Stddev Latency: 3.80038 Max latency: 19.503 Min latency: 3.19824Execute a sequential read test for 10 seconds to the storage pool:
# rados bench -p testbench 10 seq
Example Output
sec Cur ops started finished avg MB/s cur MB/s last lat avg lat 0 0 0 0 0 0 - 0 Total time run: 0.804869 Total reads made: 28 Read size: 4194304 Bandwidth (MB/sec): 139.153 Average Latency: 0.420841 Max latency: 0.706133 Min latency: 0.0816332
Execute a random read test for 10 seconds to the storage pool:
# rados bench -p testbench 10 rand
Example Output
sec Cur ops started finished avg MB/s cur MB/s last lat avg lat 0 0 0 0 0 0 - 0 1 16 46 30 119.801 120 0.440184 0.388125 2 16 81 65 129.408 140 0.577359 0.417461 3 16 120 104 138.175 156 0.597435 0.409318 4 15 157 142 141.485 152 0.683111 0.419964 5 16 206 190 151.553 192 0.310578 0.408343 6 16 253 237 157.608 188 0.0745175 0.387207 7 16 287 271 154.412 136 0.792774 0.39043 8 16 325 309 154.044 152 0.314254 0.39876 9 16 362 346 153.245 148 0.355576 0.406032 10 16 405 389 155.092 172 0.64734 0.398372 Total time run: 10.302229 Total reads made: 405 Read size: 4194304 Bandwidth (MB/sec): 157.248 Average Latency: 0.405976 Max latency: 1.00869 Min latency: 0.0378431
To increase the number of concurrent reads and writes, use the
-toption, which the default is 16 threads. Also, the-bparameter can adjust the size of the object being written. The default object size is 4MB. A safe maximum object size is 16MB. Red Hat recommends running multiple copies of these benchmark tests to different pools. Doing this shows the changes in performance from multiple clients.Add the
--run-name <label>option to control the names of the objects that get written during the benchmark test. Multiplerados benchcommands may be ran simultaneously by changing the--run-namelabel for each running command instance. This prevents potential I/O errors that can occur when multiple clients are trying to access the same object and allows for different clients to access different objects. The--run-nameoption is also useful when trying to simulate a real world workload. For example:# rados bench -p testbench 10 write -t 4 --run-name client1
Example Output
Maintaining 4 concurrent writes of 4194304 bytes for up to 10 seconds or 0 objects Object prefix: benchmark_data_node1_12631 sec Cur ops started finished avg MB/s cur MB/s last lat avg lat 0 0 0 0 0 0 - 0 1 4 4 0 0 0 - 0 2 4 6 2 3.99099 4 1.94755 1.93361 3 4 8 4 5.32498 8 2.978 2.44034 4 4 8 4 3.99504 0 - 2.44034 5 4 10 6 4.79504 4 2.92419 2.4629 6 3 10 7 4.64471 4 3.02498 2.5432 7 4 12 8 4.55287 4 3.12204 2.61555 8 4 14 10 4.9821 8 2.55901 2.68396 9 4 16 12 5.31621 8 2.68769 2.68081 10 4 17 13 5.18488 4 2.11937 2.63763 11 4 17 13 4.71431 0 - 2.63763 12 4 18 14 4.65486 2 2.4836 2.62662 13 4 18 14 4.29757 0 - 2.62662 Total time run: 13.123548 Total writes made: 18 Write size: 4194304 Bandwidth (MB/sec): 5.486 Stddev Bandwidth: 3.0991 Max bandwidth (MB/sec): 8 Min bandwidth (MB/sec): 0 Average Latency: 2.91578 Stddev Latency: 0.956993 Max latency: 5.72685 Min latency: 1.91967Remove the data created by the
rados benchcommand:# rados -p testbench cleanup
7.3. Block Device
Ceph includes the rbd bench-write command to test sequential writes to the block device measuring throughput and latency. The default byte size is 4096, the default number of I/O threads is 16, and the default total number of bytes to write is 1 GB. These defaults can be modified by the --io-size, --io-threads and --io-total options respectively. For more information on the rbd command, see the Block Device Commands section in the Ceph Block Device Guide for Red Hat Ceph Storage 3.
Creating a Ceph Block Device
As
root, load therbdkernel module, if not already loaded:# modprobe rbd
As
root, create a 1 GBrbdimage file in thetestbenchpool:# rbd create image01 --size 1024 --pool testbench
NoteWhen creating a block device image these features are enabled by default:
layering,object-map,deep-flatten,journaling,exclusive-lock, andfast-diff.On Red Hat Enterprise Linux 7.2 and Ubuntu 16.04, users utilizing the kernel RBD client will not be able to map the block device image. You must first disable all these features, except,
layering.Syntax
# rbd feature disable <image_name> <feature_name>
Example
# rbd feature disable image1 journaling deep-flatten exclusive-lock fast-diff object-map
Using the
--image-feature layeringoption on therbd createcommand will only enablelayeringon newly created block device images.This is a known issue, see the Red Hat Ceph Storage 3.3 Release Notes. for more details.
All these features will work for users utilizing the user-space RBD client to access the block device images.
As
root, map the image file to a device file:# rbd map image01 --pool testbench --name client.admin
As
root, create anext4file system on the block device:# mkfs.ext4 /dev/rbd/testbench/image01
As
root, create a new directory:# mkdir /mnt/ceph-block-device
As
root, mount the block device under/mnt/ceph-block-device/:# mount /dev/rbd/testbench/image01 /mnt/ceph-block-device
Execute the write performance test against the block device
# rbd bench-write image01 --pool=testbench
Example
bench-write io_size 4096 io_threads 16 bytes 1073741824 pattern seq
SEC OPS OPS/SEC BYTES/SEC
2 11127 5479.59 22444382.79
3 11692 3901.91 15982220.33
4 12372 2953.34 12096895.42
5 12580 2300.05 9421008.60
6 13141 2101.80 8608975.15
7 13195 356.07 1458459.94
8 13820 390.35 1598876.60
9 14124 325.46 1333066.62
..
