crimson

Crimson is the code name of crimson-osd, which is the next generation ceph-osd. It targets fast networking devices, fast storage devices by leveraging state of the art technologies like DPDK and SPDK, for better performance. And it will keep the support of HDDs and low-end SSDs via BlueStore. Crismon will try to be backward compatible with classic OSD.

Running Crimson

As you might expect, crimson is not featurewise on par with its predecessor yet.

daemonize

Unlike ceph-osd, crimson-osd does daemonize itself even if the daemonize option is enabled. Because, to read this option, crimson-osd needs to ready its config sharded service, but this sharded service lives in the seastar reactor. If we fork a child process and exit the parent after starting the Seastar engine, that will leave us with a single thread which is the replica of the thread calls fork(). This would unnecessarily complicate the code, if we would have tackled this problem in crimson.

Since a lot of GNU/Linux distros are using systemd nowadays, which is able to daemonize the application, there is no need to daemonize by ourselves. For those who are using sysvinit, they can use start-stop-daemon for daemonizing crimson-osd. If this is not acceptable, we can whip up a helper utility to do the trick.

logging

Currently, crimson-osd uses the logging utility offered by Seastar. see src/common/dout.h for the mapping between different logging levels to the severity levels in Seastar. For instance, the messages sent to derr will be printed using logger::error(), and the messages with debug level over 20 will be printed using logger::trace().

ceph seastar
< 0 error
0 warn
[1, 5) info
[5, 20] debug
> 20 trace

Please note, crimson-osd does not send the logging message to specified log_file. It writes the logging messages to stdout and/or syslog. Again, this behavior can be changed using --log-to-stdout and --log-to-syslog command line options. By default, log-to-stdout is enabled, and the latter disabled.

vstart.sh

To facilitate the development of crimson, following options would be handy when using vstart.sh,

--crimson
start crimson-osd instead of ceph-osd
--nodaemon
do not daemonize the service
--redirect-output
redirect the stdout and stderr of service to out/$type.$num.stdout.
--osd-args
pass extra command line options to crimson-osd or ceph-osd. It’s quite useful for passing Seastar options to crimson-osd.

So, a typical command to start a single-crimson-node cluster is:

MGR=1 MON=1 OSD=1 MDS=0 RGW=0 ../src/vstart.sh -n -x --without-dashboard --memstore \
  --crimson --nodaemon --redirect-output \
  --osd-args "--memory 4G --smp 1 --cpuset 0"

Where we assign 4 GiB memory, a single thread running on core-0 to crimson-osd. Please refer crimson-osd --help-seastar for more Seastar specific command line options.

You could stop the vstart cluster using:

../src/stop.sh --crimson

Debugging Crimson

debugging tips

When a seastar application crashes, it leaves us a serial of addresses, like:

Segmentation fault.
Backtrace:
0x00000000108254aa
0x00000000107f74b9
0x00000000105366cc
0x000000001053682c
0x00000000105d2c2e
0x0000000010629b96
0x0000000010629c31
0x00002a02ebd8272f
0x00000000105d93ee
0x00000000103eff59
0x000000000d9c1d0a
/lib/x86_64-linux-gnu/libc.so.6+0x000000000002409a
0x000000000d833ac9
Segmentation fault

seastar-addr2line offered by Seastar can be used to decipher these addresses. After running the script, it will be waiting for input from stdin, so we need to copy and paste the above addresses, then send the EOF by inputting control-D in the terminal:

$ ../src/seastar/scripts/seastar-addr2line -e bin/crimson-osd

0x00000000108254aa
0x00000000107f74b9
0x00000000105366cc
0x000000001053682c
0x00000000105d2c2e
0x0000000010629b96
0x0000000010629c31
0x00002a02ebd8272f
0x00000000105d93ee
0x00000000103eff59
0x000000000d9c1d0a
0x00000000108254aa
[Backtrace #0]
seastar::backtrace_buffer::append_backtrace() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1136
seastar::print_with_backtrace(seastar::backtrace_buffer&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1157
seastar::print_with_backtrace(char const*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:1164
seastar::sigsegv_action() at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5119
seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::operator()(int, siginfo_t*, void*) const at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5105
seastar::install_oneshot_signal_handler<11, &seastar::sigsegv_action>()::{lambda(int, siginfo_t*, void*)#1}::_FUN(int, siginfo_t*, void*) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5101
?? ??:0
seastar::smp::configure(boost::program_options::variables_map, seastar::reactor_config) at /home/kefu/dev/ceph/build/../src/seastar/src/core/reactor.cc:5418
seastar::app_template::run_deprecated(int, char**, std::function<void ()>&&) at /home/kefu/dev/ceph/build/../src/seastar/src/core/app-template.cc:173 (discriminator 5)
main at /home/kefu/dev/ceph/build/../src/crimson/osd/main.cc:131 (discriminator 1)