tuning for maximum dhcp performance

Blake Hudson blake at ispn.net
Fri May 2 13:42:39 UTC 2008

I was using ext3. For all the touted performance advantages of reiserfs, 
and thought that ext3 is 'old' or 'outdated', ext3 still provides 
reliable, fast, and consistent results for the server workloads we see 
in actual use.

There may be tasks where one file system is drastically better than 
another, but for general use I'm pretty happy with ext3.

-------- Original Message  --------
Subject: Re: tuning for maximum dhcp performance
From: Dan <dan at telcohero.com>
To: dhcp-users at isc.org
Date: Thursday, May 01, 2008 3:02:36 PM
> 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.

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