tuning for maximum dhcp performance

Dan dan at telcohero.com
Sat Apr 26 02:43:40 UTC 2008

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 simultaneously,
> 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 to
> 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 Behalf
> 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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