Question

Script to prevent a ZFS hang.

Asked by: p0sreed

I have an open solaris sun machine that encounters a zfs file system hang most of the time.

When we issue ZFS list , it hangs in there with no result. I have to execute "echo | format" or the "format" command to clear the hang.

I want to write a perl script that automates this every time the zfs filesystem hangs. The algorithm is below.

1. execute "zfs list | wc -l" and store the value in a scalar
2. check scalar is empty or not
3. if scalar value is empty, execute "echo | format " command
4. else exit

Want to set up this script as a crob job to run eveery minute

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Asked On
2009-07-21 at 12:27:06ID24588705
Topics

Perl Programming Language

,

Sun Solaris

Participating Experts
2
Points
500
Comments
11

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Answers

 

by: clockwatcherPosted on 2009-07-21 at 12:45:20ID: 24908533

Can you show the output of your 'zfs list | wc -l' in your two scenarios (one where it's working, the other where it's hung?).  With it, you can probably get a more definitive answer, without it maybe this:

#!/usr/bin/perl
system("echo | format") if `zfs list | wc -l`;

                                              
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2:

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by: p0sreedPosted on 2009-07-21 at 12:51:03ID: 24908605

The problem with that script is that. "zfs list | wc -l" will hang itself, will not give any result to the test and non-execution of the command.

 

by: clockwatcherPosted on 2009-07-21 at 12:51:13ID: 24908608

Sorry... meant:

 #!/usr/bin/perl
system("echo | format") unless `zfs list | wc -l`;
 

                                              
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by: p0sreedPosted on 2009-07-21 at 12:53:58ID: 24908644

Where will the output of "echo | format" go to?

 

by: clockwatcherPosted on 2009-07-21 at 12:54:01ID: 24908645

So it's really not:

1. execute "zfs list | wc -l" and store the value in a scalar
2. check scalar is empty or not
3. if scalar value is empty, execute "echo | format " command
4. else exit

It's:

1. execute "zfs list | wc -l"
2. if it hangs, execute "echo | format " command
4. else exit

Correct?  How long of a wait before you consider it hung?  A few seconds?

 

by: p0sreedPosted on 2009-07-21 at 12:59:59ID: 24908701

yes, correct. I would give it 10 seconds to produce an output, else it is hung, or the other hand, using "wc -l" was to rule out a timeout, if "wc -l" doesn't produce a number, we can execute the format command

 

by: clockwatcherPosted on 2009-07-21 at 13:23:58ID: 24908940

Try:

eval {
        local $SIG{ALRM} = sub { system("echo | format"); exit; };
        alarm 10;
        $data = `zfs list`;
};
if ($@) {
        print "Error: $@\n";
}
                                              
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by: p0sreedPosted on 2009-07-21 at 13:29:49ID: 24909004

Thank you. I really have no way of testing this script as i don't have a system hang at the moment. If you do, please, let me know. I will implement this script in the cron and monitor the system for a week and get back to you otherwise

 

by: clockwatcherPosted on 2009-07-21 at 13:38:07ID: 24909079

I tested it with a command that sleeps for 60 seconds (rather than zfs) and it worked, but YMMV.  I'm fairly certain the timeout on the alarm will catch the hang, but I'm not so sure about the echo | format clearing your zfs problem via the perl script within a cron job.  Give it a try and let us know.

BTW,forgot to include the shebang in the code I posted.  If you're calling it directly, don't forget it-- like I did.  :-)

 

by: bluPosted on 2009-07-31 at 05:57:12ID: 24988295

You should report this as it is a bug. The next time you have a hang in zfs list, run this command as root:

mdb -k <<EOF
::pgrep zfs | ::walk thread | ::findstack
EOF

Post the output along with the output of "uname -a"

20120131-EE-VQP-002

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