tuning for maximum dhcp performance

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


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

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 

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.

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