full socket buffers

[Glenn Satchell]

On 02/05/11 04:16, Mirek Lauš wrote:
> Hello again,
>
> On Sat, Dec 18, 2010 at 10:53 PM,<sthaug at nethelp.no>  wrote:
>>>> We're also running 4.1.1p1, on FreeBSD 7.3-STABLE. Server hardware is
>>>> Dell PE 1850, with two SCSI disks in a RAID-1 configuration. We have
>>>> around 100k leases on two servers in a failover pair, with most of the
>>>> pools on 24 hour leasetime. We don't see the problem you're seeing.
>>>
>>> We're running the dhcpd service on two IBM x3550 servers in failover,
>>> both have two 74GB 15k disks in RAID-1 so very similar to yours.
>>
>> How many DISCOVERs and REQUESTs do you handle per second? Do you have
>> battery backed cache for your RAID-1 config? Have you tried gstat, and
>> looked at the %busy column?
>>
>> An additional point which might be relevant - we run our failover
>> configuration with a "delayed-ack 28" setting. This cuts down on the
>> failover traffic (including disk I/O). Yes, we know there have been
>> some warnings about delayed-ack - however it has never given us any
>> problems. Note that it needs to be explicitly compiled in.
>
> we have upgraded our RAID controller to ServeRAID 8k with 256MB write-back
> cache. Few days later we have encountered the issue again. The kernel starts
> to drop UDP packets due to "full socket buffers". Only solution to
> this situation
> is a dhcpd process restart. I'm pointless. What would you recommend to trace
> down the cause of the issue?
>
> Regards,
> Miroslav

This is an operating system setting. Try google for your OS and 
something like "set udp buffer size".

-- 
regards,
-glenn