full socket buffers

[Mirek Lauš]

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