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Chapter 9. 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.

9.1. Performance Baseline
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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, please view Red Hat’s Knowledgebase article on the subject.

9.2. Storage Cluster
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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.

Create a new storage pool:

ceph osd pool create testbench 100 100
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Note

Before running these performance tests, drop all the file system caches by running the following: 

sudo echo 3 | sudo tee /proc/sys/vm/drop_caches && sudo sync
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Execute a write test for 10 seconds to the newly created storage pool:

rados bench -p testbench 10 write --no-cleanup
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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:            3.19824
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Execute a sequential read test for 10 seconds to the storage pool:

rados bench -p testbench 10 seq
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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
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Execute a random read test for 10 seconds to the storage pool:

rados bench -p testbench 10 rand
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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
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To increase the number of concurrent reads and writes, use the -t option, which the default is 16 threads. Also, the -b parameter can adjust the size of the object being written. The default object size is 4MB. 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. Multiple rados bench commands may be ran simultaneously by changing the --run-name label 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-name option is also useful when trying to simulate a real world workload. For example: 

rados bench -p testbench 10 write -t 4 --run-name client1
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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:            1.91967
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Remove the data created by the rados bench command:

rados -p testbench cleanup
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9.3. Block Device
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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 Ceph Block Device Guide.

Creating a Ceph Block Device

  1. Load the rbd kernel module, if not already loaded: 

    sudo modprobe rbd
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  2. Create a 1 GB rbd image file in the testbench pool: 

    sudo rbd create image01 --size 1024 --pool testbench
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  3. Map the image file to a device file: 

    sudo rbd map image01 --pool testbench --name client.admin
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  4. Create an ext4 file system on the block device: 

    sudo mkfs -t ext4 -m0 /dev/rbd/testbench/image01
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  5. Create a new directory: 

    sudo mkdir /mnt/ceph-block-device
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  6. Mount the block device under /mnt/ceph-block-device/: 

    sudo mount /dev/rbd/testbench/image01 /mnt/ceph-block-device
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Execute the write performance test against the block device:

rbd bench-write image01 --pool=testbench
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Example output: 

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
    ..
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