system freezes.

[Chad Leigh -- Shire.Net LLC]

> At 10:56 AM 5/22/2006, Brent Rieck wrote:
>> Hello,
>>   I've been having some freeze problems with my "managed" freebsd  
>> server
>> that my host has been less than helpful with; I hope that this is the
>> right place to ask the questions I have.
>>
>> os: freebsd 4.8-stable
>> major applications: apache 1.3.29 + php 4.3.10 , mysql 4.1.18-log,
>> dirvish, riff-backup
>>
>>   Machine freezes with nothing written to the logs or console - if  
>> you
>> happen to be logged in and running top when it "starts" to freeze  
>> your
>> top session will run completely normally and without lag (spacebar
>> refreshes display, you can resort on size or cpu, etc), but no other
>> processes can start - typing a command into another open shell  
>> will not
>> start that program.  Until it fully freezes it will echo  
>> characters back
>> in the shell - and top will continue to run as normal.  Top always  
>> shows
>> a load of <0.1, there's always 5MB to 50MB of ram free.
>>
>>   All of the hardware has been replaced (motherboard, cpu, ram, power
>> supply, hard drive)
>>
>>   I can't make it freeze on demand by replaying the web hits or  
>> database
>> queries that occurred before the crash.
>>
>>   I am able to make it freeze on demand by slurping down a particular
>> dirvish vault with rsync.  The freeze symptoms are the same as the
>> random freeze symptoms (top responds normally, new processes can't  
>> start)
>>
>>   The random freezes occur whether or not I'm running dirvish on a  
>> schedule.
>>
>>   The rsync freezing I can work around if needed, the random  
>> freezes I
>> cannot.  Does anybody have any suggestions on how I might track  
>> down the
>> problem?
>>
>> thanks,
>> Brent

This sounds like some sort of IO is not finishing and other processes  
are getting stuck in a queue behind the process with the "stuck" IO.

I have a similar issue 5.3-6.0 that has been bedeviling  me very  
infrequently with some md file backed images mounted as /dev/md*  
devices.

Chad


---
Chad Leigh -- Shire.Net LLC
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chad at shire.net