Linux bind / dhcp iowait status

Tom Greaser tgreaser at
Fri Mar 17 12:45:45 UTC 2006

Thanks David.. I will test to see this is my issue..
but its sounds like it is.. THANKS!!

>>>David_Hankins at 03/16/06 4:30 pm >>> 
On Wed, Mar 15, 2006 at 09:42:17AM -0500, Tom Greaser wrote: 
>Its an Redhat AS 4 update 3 box with mirrored scsi Ultra 320 drives 
Most Linux syslog implementations fsync() after every log message was 
written before moving on to process the next one. 
I've seen this cause problems because eventually the syslog buffers can 
fill, and the applications that are trying to log wind up sleeping when 
they try to call syslog(). 
We fsync() before a lease is offered to a client.  We do this because 
of the way we interpret RFC2131 (some other implementations don't). 
BIND also fsync()'s journal files before it responds to a DNS update 
request.  For very much the same reason...don't say "Yes" unless you 
would give the same answer after a reboot. 
If syslog is also calling fsync(), it will do it multiple times 
inbetween both DHCP's and BIND's.  It multiplies your overhead. 
At any rate, have a look at your syslog.conf, and if you are funneling 
BIND and DHCP traffic through it, try looking at your syslog's manpage 
('syslog.conf' versions will differ from syslog-ng versions) to see 
what it's doing. 
In the syslog.conf case, you might want to configure a - before the 
filename (or whatever your manpage says): 
      You  may  prefix  each  entry with the minus ``-'' sign to 
      omit syncing the file after every logging.  Note that  you 
      might  lose information if the system crashes right behind 
      a write attempt.  Nevertheless this might  give  you  back 
      some  performance, especially if you run programs that use 
      logging in a very verbose manner. 
I'm not familiar enough with syslog-ng offhand. 
David W. Hankins"If you don't do it right the first time, 
Software Engineeryou'll just have to do it again." 
Internet Systems Consortium, Inc.-- Jack T. Hankins 

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