Welcome to the Free Software contributions diary of Loïc Dachary. Although the posts look like blog entries, they really are technical reports about the work done during the day. They are meant to be used as a reference by co-developers and managers.

List the versions of OSDs in a Ceph cluster

List the versions that each OSD in a Ceph cluster is running. It is handy to find out how mixed the cluster is.

# ceph tell osd.* version
osd.0: { "version": "ceph version 0.67.4 (ad85ba8b6e8252fa0c7)"}
osd.1: { "version": "ceph version 0.67.5 (a60acafad6096c69bd1)"}
osd.3: Error ENXIO: problem getting command descriptions from osd.3
osd.6: { "version": "ceph version 0.72.2 (a913ded64099cfd60)"}
osd.7: { "version": "ceph version 0.72.1 (4d923874997322de)"}
osd.8: { "version": "ceph version 0.72.1 (4d923874997322de)"}
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HOWTO extract a stack trace from teuthology

When a teuthology test suite fails on Ceph, it shows in pulpito. For instance there is one failure in the monthrash test suite with details and a link to the logs. By removing the teuthology.log part of the link a directory listing shows all informations archived for this run are available.
In the example above the logs show:

client.0.plana34.stderr:+ ceph_test_rados_api_io
client.0.plana34.stdout:Running main() from gtest_main.cc
client.0.plana34.stdout:[==========] Running 43 tests from 4 test cases.
client.0.plana34.stdout:[----------] Global test environment set-up.
client.0.plana34.stdout:[----------] 11 tests from LibRadosIo
client.0.plana34.stdout:[ RUN      ] LibRadosIo.SimpleWrite
client.0.plana34.stdout:[       OK ] LibRadosIo.SimpleWrite (1509 ms)
client.0.plana34.stdout:[ RUN      ] LibRadosIo.ReadTimeout
client.0.plana34.stderr:Segmentation fault (core dumped)

That shows ceph_test_rados_api_io is running from the plana34 machine and core dumped and the remote/plana34/coredump subdirectory contains the corresponding core dump.
The teuthology logs show the repository from which the binary was downloaded (it was produced by gitbuilder).

echo deb http://gitbuilder.ceph.com/ceph-deb-precise-x86_64-basic/sha1/f5c1d3b6988bae5ffb914d2ac0b2858caeffe12c precise main | sudo tee /etc/apt/sources.list.d/ceph.list

and running this line on an Ubuntu precise 12.04 64bits as suggested by the name of the subdirectory precise-x86_64 will make the corresponding binary packages available. It is also possible to download them directly from the pool/main/c/ceph subdirectory. The packages that are suffixed with -dbg retain the debug symbols that are necessary for gdb to display an informative stack trace.
The ceph_test_rados_api_io binary is part of the ceph-test package and can be extracted with

$ dpkg --fsys-tarfile ceph-test_0.85-726-gf5c1d3b-1precise_amd64.deb | \
  tar xOf -  ./usr/bin/ceph_test_rados_api_io \
  > ceph_test_rados_api_io

and the stack trace displayed with

$ gdb /usr/bin/ceph_test_rados_api_io 1411176209.8835.core
(gdb) bt
#0  0x00007f541b95750a in pthread_rwlock_wrlock () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00007f541bd41341 in RWLock::get_write(bool) () from /usr/lib/librados.so.2
#2  0x00007f541bd2bbc9 in Objecter::op_cancel(Objecter::OSDSession*, unsigned long, int) () from /usr/lib/librados.so.2
#3  0x00007f541bcf1349 in Context::complete(int) () from /usr/lib/librados.so.2
#4  0x00007f541bdad5ea in RWTimer::timer_thread() () from /usr/lib/librados.so.2
#5  0x00007f541bdb149d in RWTimerThread::entry() () from /usr/lib/librados.so.2
#6  0x00007f541b953e9a in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#7  0x00007f541b16a3fd in clone () from /lib/x86_64-linux-gnu/libc.so.6
#8  0x0000000000000000 in ?? ()
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Running python rados tests in Ceph

When Ceph is built from sources, make check will not run the test_rados.py tests.
A minimal cluster is required and can be run from the src directory with:

CEPH_NUM_MON=1 CEPH_NUM_OSD=3 ./vstart.sh -d -n -X -l mon osd

The test can then be run with

$ PYTHONPATH=pybind nosetests -v

and if only the TestIoctx.test_aio_read is of interest, it can be appended to the filename:

$ PYTHONPATH=pybind nosetests -v
test_rados.TestIoctx.test_aio_read ... ok

Ran 1 test in 4.227s

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t540p touchpad disable mouse, keep buttons

To use the touchpad to click (but not to move the mouse) and keep using the trackpad for mouse movement:

synclient AreaBottomEdge=1
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Ceph placement group memory footprint, in debug mode

A Ceph cluster is run from sources with

CEPH_NUM_MON=1 CEPH_NUM_OSD=5 ./vstart.sh -d -n -X -l mon osd

and each ceph-osd uses approximately 50MB of resident memory

loic      7489  1.7  0.2 586080 43676 ?        Ssl  17:55   0:01  ceph-osd
loic      7667  1.6  0.2 586080 43672 ?        Ssl  17:55   0:01  ceph-osd

A pool is created with 10,000 placement groups

$ ceph osd pool create manypg 10000
pool 'manypg' created

the creation completes within half an hour

$ ceph -w
2014-09-19 17:57:35.193706 mon.0 [INF] pgmap v40: 10152
   pgs: 10000 creating, 152 active+clean; 0 bytes data, 808 GB used, 102 GB / 911 GB avail
2014-09-19 18:35:08.668877 mon.0 [INF] pgmap v583: 10152
   pgs: 46 active, 10106 active+clean; 0 bytes data, 815 GB used, 98440 MB / 911 GB avail
2014-09-19 18:35:13.505841 mon.0 [INF] pgmap v584: 10152
   pgs: 10152 active+clean; 0 bytes data, 815 GB used, 98435 MB / 911 GB avail

The OSD now use approximately 150MB which suggests that each additional placement group uses ~10KB of resident memory.

loic      7489  0.7  1.0 725952 166144 ?       Ssl  17:55   2:02 ceph-osd
loic      7667  0.7  0.9 720808 160440 ?       Ssl  17:55   2:03 ceph-osd
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Running node-rados from sources

The nodejs rados module comes with an example that requires a Ceph cluster.
If Ceph was compiled from source, a cluster can be run from the source tree with

rm -fr dev out ;  mkdir -p dev
 ./vstart.sh -d -n -X -l mon osd

It can be used by modifying the /etc/ceph/ceph.conf in the example to the one from the sources : $CEPHSOURCE/src/ceph.conf. The expected output is

$ node exemple.js
fsid : c041968a-a895-4a5c-a0a7-6621e08a4f07
ls pools : rbd
 --- RUN Sync Write / Read ---
Read data : 01234567ABCDEF
 --- RUN ASync Write / Read ---
 --- RUN Attributes Write / Read ---
testfile3 xattr = {"attr1":"first attr","attr2":"second attr","attr3":"last attr value"}
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HOWTO test a Ceph crush rule

The crushtool utility can be used to test Ceph crush rules before applying them to a cluster.

$ crushtool --outfn crushmap --build --num_osds 10 \
   host straw 2 rack straw 2 default straw 0
# id	weight	type name	reweight
-9	10	default default
-6	4		rack rack0
-1	2			host host0
0	1				osd.0	1
1	1				osd.1	1
-2	2			host host1
2	1				osd.2	1
3	1				osd.3	1
-7	4		rack rack1
-3	2			host host2
4	1				osd.4	1
5	1				osd.5	1
-4	2			host host3
6	1				osd.6	1
7	1				osd.7	1
-8	2		rack rack2
-5	2			host host4
8	1				osd.8	1
9	1				osd.9	1	

Creates a crushmap from scratch (–build). It assumes there is a total of 10 OSDs available ( –num_osds 10 ). It then places two OSDs in each host ( host straw 2 ). The resulting hosts (five of them) are then placed in racks, at most two per racks ( rack straw 2 ). All racks are placed in the default root (that’s what the zero stands for : all of them) ( default straw 0 ). The last rack only has one host because there is an odd number of hosts available.
The crush rule to be tested can be injected in the crushmap with

crushtool --outfn crushmap --build --num_osds 10 host straw 2 rack straw 2 default straw 0
crushtool -d crushmap -o crushmap.txt
cat >> crushmap.txt <<EOF
rule myrule {
	ruleset 1
	type replicated
	min_size 1
	max_size 10
	step take default
	step choose firstn 2 type rack
	step chooseleaf firstn 2 type host
	step emit
crushtool -c crushmap.txt -o crushmap

This crushmap should be able to provide two OSDs ( for placement groups for instance ) and it can be verified with the –test option.

$ crushtool -i crushmap --test --show-statistics --rule 1 --min-x 1 --max-x 2 --num-rep 2
rule 1 (myrule), x = 1..2, numrep = 2..2
CRUSH rule 1 x 1 [0,2]
CRUSH rule 1 x 2 [7,4]
rule 1 (myrule) num_rep 2 result size == 2:	2/2

The –rule 1 designates the rule that was injected. The –rule 0 is the default rule that is created by default. The x can be thought of as the unique name of the placement group for which OSDs are reclaimed. The –min-x 1 –max-x 2 varies the value of x from 1 to 2 therefore trying the rule only twice. –min-x 1 –max-x 2048 would create 2048 lines. Each line shows the value of x after the rule number. In rule 1 x 2 the 1 is the rule number and the 2 is the value of x. The last line shows that for all values of x (2/2 i.e. 2 values of x out of 2), when asked to provide 2 OSDs (num_rep 2) the crush rule was able to provide 2 (result size == 2).

If asked for 4 OSDs, the same crush rule may fail because it has barely enough resources to satisfy the requirements.

$ crushtool -i crushmap --test --show-statistics --rule 1 --min-x 1 --max-x 2 --num-rep 4
rule 1 (myrule), x = 1..2, numrep = 4..4
CRUSH rule 1 x 1 [0,2,9]
CRUSH rule 1 x 2 [7,4,1,3]
rule 1 (myrule) num_rep 4 result size == 3:	1/2
rule 1 (myrule) num_rep 4 result size == 4:	1/2

The statistics at the end shows that one of the two mappings failed: the result size == 3 is lower than the required number num_rep 4. If asked for more OSDs than the rule can provide, the rule will always fail.

crushtool -i crushmap --test --show-statistics --rule 1 --min-x 1 --max-x 2 --num-rep 5
rule 1 (myrule), x = 1..2, numrep = 5..5
CRUSH rule 1 x 1 [0,2,9]
CRUSH rule 1 x 2 [7,4,1,3]
rule 1 (myrule) num_rep 5 result size == 3:	1/2
rule 1 (myrule) num_rep 5 result size == 4:	1/2

More examples of crushtool usage can be found in the crushtool directory of the Ceph sources.

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HOWTO test teuthology tasks

The Ceph integration tests run by teuthology are described with YAML files in the ceph-qa-suite repository. The actual work is carried out on machines provisioned by teuthology via tasks. For instance, the workunit task runs a script found in the qa/workunits directory of the Ceph repository.
The workunit.py script, although small, is complex enough to deserve testing. Creating unit tests would require a lot of mocking and it would not catch a typo in a shell command to be run on an actual machine. Another approach is to create light weight integration tests within the ceph-qa-suite repository itself. For instance tests/workunit is designed to maximize coverage of the workunit.py script and run as quickly as possible.
Continue reading

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What cinder volume is missing an RBD object ?

Although it is extremely unlikely to loose an object stored in Ceph, it is not impossible. When it happens to a Cinder volume based on RBD, knowing which has an object missing will help with disaster recovery.
Continue reading

Posted in Havana, ceph, openstack | Leave a comment

Tell teuthology to use a local ceph-qa-suite directory

By default teuthology will clone the ceph-qa-suite repository and use the tasks it contains. If tasks have been modified localy, teuthology can be instructed to use a local directory by inserting something like:

suite_path: /home/loic/software/ceph/ceph-qa-suite

in the teuthology job yaml file. The directory must then be added to the PYTHONPATH

PYTHONPATH=/home/loic/software/ceph/ceph-qa-suite \
   ./virtualenv/bin/teuthology  --owner loic@dachary.org \
   /tmp/work.yaml targets.yaml
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