tuning for maximum dhcp performance

Frank Bulk - iNAME frnkblk at iname.com
Sat Apr 26 03:59:43 UTC 2008

Would you be willing to describe your node environment that would facilitate
them coming online at the "same time"?  What kind of maintenance window
would cause 10,000 nodes to do that?


-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf
Of Dan
Sent: Friday, April 25, 2008 9:44 PM
To: dhcp-users at isc.org
Subject: RE: tuning for maximum dhcp performance

I could easily lose up to almost 10,000 nodes at once and have them all
come online at effectively the same time.  This could, and will I'm sure,
occur during a maintenance window.

I'd like to make the most of what I have.

On Fri, 25 Apr 2008, Frank Bulk - iNAME wrote:

> I serve up 10,000 leases ranging from 3 to 14 days.  I haven't spent a
> second optimizing it.  It just works and has worked no matter what the
> client outage conditions have been.
> Unless you're serving up a campus where there is a real possibility that
> thousands of like clients (i.e. VoIP phone) may power up and come back
> online, there's no need to spend time over-engineering.  If there were 20k
> computers on a campus that lost power and power came back on
> many of the PCs would stay off (configured in the BIOS), and those
> configured to power on after power failure would reach the DHCP request
> phase at different spots.  At 80/second, it would take just a bit over 4
> minutes to serve them all (if the requests were linear).  Would it really
> matter if in the worst of all cases it took 10 minutes for every client to
> be back online?
> It's those networks that serve hundreds of thousands of clients that need
> spend time engineering a solution that serves up IPs in a timely fashion.
> Frank
> -----Original Message-----
> From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On
> Of Dan
> Sent: Friday, April 25, 2008 1:01 PM
> To: dhcp-users at isc.org
> Subject: tuning for maximum dhcp performance
> I'm currently constructing a replacement for an old Cisco Network
> Registrar setup serving about 20,000 nodes (10,000 with 24hr leases,
> 10,000 with 7day leases).
> I'm running Linux 2.6.22 using ISC DHCPd 3.0.5 with dhcp-3.0.5-ldap-patch
> and dhcp-3.0.5-next-file.patch.  I hope to use failover between the 2
> servers, but haven't worked on that yet.
> As stated time and again, the software will not be the bottleneck. Using
> dhcpref's discovery benchmark, I'm seeing about 80 clients/second right
> now with my new hardware (ping-check off).  When I disable the per-lease
> fsync or move the dhcpd.leases file to ramdisk, it jumps to well over 400
> clients/second limited by CPU.
> My hardware is 2 servers with the following spec:
>   Dell PowerEdge 2970
>   Dual-core 2Ghz 64bit AMD
>   4G RAM
>   10k RAID1 System Drives
>   15k RAID10 Storage Drives (just for dhcpd.leases file)
> Do anyone have any pointers on running a system like this and achieving
> maximum dhcp performance?
> Some factors that come to mind are:
>   -Other patches I should/could be using?
>   -Raid stripe element size, read-ahead, and write-back?
>      (currently 64Kb, no, and yes)
>   -Filesystem choice for dhcpd.leases file?
>      (ext3, reiserfs, xfs, jfs -- currently resierfs)
>   -Filesystem parameters to tune?
>   -Kernel parameters to tune?
> Having a better understanding about how DHCPd works with the dhcpd.leases
> file might give me some of the answers to these questions also.
> Any information or shared experiences would be greatly appreciated.
> Thanks,
> Dan

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