tuning for maximum dhcp performance

Brian Raaen braaen at zcorum.com
Fri Apr 25 18:21:00 UTC 2008

Dear Dan,
	As far as the filesystem goes, for the ultimate in performance you might want 
to mount /etc/dhcpd (or wherever your leases file is) to a partition in your 
RAM.  Your could rsync this folder every few minutes/hours to back it up 
depending on your needs.  That would keep you from being harddrive bound. 

Brian Raaen
Network Engineer
braaen at zcorum.com

On Friday 25 April 2008, Dan wrote:
> 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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