tuning for maximum dhcp performance

[Brian Raaen]

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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