tuning for maximum dhcp performance

Dan dan at telcohero.com
Thu May 1 20:02:36 UTC 2008


Blake,

Write-back was on, I confirmed.  Even so, I was still unable to get 
numbers approaching the ramdisk until I started trying different 
filesystems.

It seems that when starting dhcp with a blank dhcpd.leases file, using 
reiserfs filesystem, and dhcperf, you get poor performance.  JFS, XFS, and 
even EXT3 (in descending order) all resulted in over 300 5way 
clients/second.

All filesystems were mounted with noatime, nodiratime, nodev, 
nosuid, and noexec.

I was a bit surprised that the difference was this drastic.


On Fri, 25 Apr 2008, Blake Hudson wrote:

> Dan, are you sure you have the RAID controller cache activated (write back) 
> on the leases array? I noticed performance similar to that of a RAM drive 
> (single CPU limited) when I enabled this option on our Dell servers... At 
> least, that's how I remember it....
>
> You might want to look a ways back for the posts with the subject: "Watching 
> performance on a DHCP Server"... may of the latter posts are by people who 
> didn't read the thread's beginnings and didn't really seem to get the point, 
> but the bulk of the thread seems to pertains to exactly what you're asking 
> and looking for.
>
> http://marc.info/?t=119498963900004&r=2&w=2
>
> -Blake
>
> -------- Original Message  --------
> Subject: Re: tuning for maximum dhcp performance
> From: Dan <dan at telcohero.com>
> To: dhcp-users at isc.org
> Date: Friday, April 25, 2008 1:47:02 PM
>> 
>> My original post comments on the performance gains of a ramdrive, but I'd 
>> be much more likely to just remove the per-lease fsync and keep it on the 
>> generator-backed, ups-backed, battery-backed raid10 which gives me almost 
>> the same performance, but without as much exposure:
>>
>>  80 clients/sec - raid10
>> 420 clients/sec - raid10 no fsync
>> 480 clients/sec - ramdisk
>> 
>> Rsycning a fairly large dhcpd.leases periodically leaves a lot of room for 
>> lost information.
>> 
>> I would still prefer keeping the fsync, although I'd be curious to know how 
>> many people are running systems without the fsync or on a ramdrive.
>> 
>> 
>> On Fri, 25 Apr 2008, Brian Raaen wrote:
>> 
>>> 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.
>>> 
>>> 
>>> 
>> 
>
>
>


More information about the dhcp-users mailing list