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Today's Topics:
1. Re: Dhcp load testing (Dave C)
2. Re: Dhcp load testing (Simon Hobson)
----------------------------------------------------------------------
Message: 1
Date: Thu, 31 Oct 2019 15:27:26 -0500
From: Dave C <d...@gvtc.drakkar.org>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>, Peter Yardley
<peter.yard...@uts.edu.au>
Subject: Re: Dhcp load testing
Message-ID: <dc6f1dab-f13a-7cfd-895a-f9b92b85b...@gvtc.drakkar.org>
Content-Type: text/plain; charset=utf-8; format=flowed
That part about sending your logs elsewhere via syslog is extremely critical.
The leases file will be an append only operation and can handle a pretty hefty
workload, as long
as the diskio subsystem isn't also dragging attention to syslog writing to
local disks several
times for _every_ dhcp transaction.
Send syslog elsewhere and it should dramatically improve performance for you.
A trick I've done in the very distant past when disk speeds were horrible was
to create a
virtual disk in ram (ramdisk), let the leases file live there and once a minute
or so, copy the
leases file to a persistent disk.
I'd think that would only be needed for extremely busy systems. I've routinely
managed leases
for around 75k files on a low powered Linux VM... but only when I turned off
local syslog :) If
you needed to manage a half million or so, maybe a ramdisk might be needed...
but at that point
I'd start looking at lease times to reduce transaction cycles and whether it
makes more sense to
split the environment to multiple DHCP servers so that you don't have as many
eggs in a single
basket (or pair of baskets in an active/active configuration). I went from a
pair of servers
each handling 75k or so leases to 5 sets of paired active/active servers each
handling about 1/4
to 1/6 of what the two combined used to have.
Dave
On 10/30/19 20:02, Peter Yardley wrote:
> Take a look at ?
>
> https://kb.isc.org/docs/aa-01283
>
> Major bottleneck is disk IO so try to speed that up (raid, flash etc). If
> using UNIX put the
> leases file in a mount point with ?noatime? enabled. Send the logs to another
> server using syslog.
>
> > On 31 Oct 2019, at 5:21 am, Kraishak Mahtha <kraishak....@gmail.com> wrote:
> >
> > Hi Everyone,
> >
> > I am using the isc dhcpd on my lab environment so before I use it to my
> workshop, I want to
> try load test on it. I created the configuration with sufficient long pool, I
> tried running
> perfdhcp tool for load testing as suggested in many google forums and I
> observed that at a
> maximum of 10-14 transactions per second(tried with other different tools
> also), If I increase
> load the packets are getting dropped, I don't think that is benchmark of ISC
> dhcp, can any one
> has idea or any suggestions of how can i increase load handling capacity of
> the dhcpd service
> > FYI: I diabled ping check
> > Ping check false;
> > Ping time out 0;
> > The above two statements already added to my config file.
> >
> >
> > Thanks
> > _______________________________________________
> > dhcp-users mailing list
> > dhcp-users@lists.isc.org <mailto:dhcp-users@lists.isc.org>
> > https://lists.isc.org/mailman/listinfo/dhcp-users
>
> ._--_|\ Peter Yardley |
> / \ Senior Network Engineer | peter.yard...@uts.edu.au
> <mailto:peter.yard...@uts.edu.au>
> \_.--._* Information Technology Division, | Ph: +61 2 9514-2358
> . v University of Technology, Sydney.| Fax: +61 2 9514-4327
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------------------------------
Message: 2
Date: Thu, 31 Oct 2019 23:24:26 +0000
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Dhcp load testing
Message-ID: <f3c3852d-f804-4080-b09c-a9bda2dbd...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii
Dave C <d...@gvtc.drakkar.org> wrote:
> That part about sending your logs elsewhere via syslog is extremely critical.
As a halfway house, configure syslog for async logging.
The default is (on every system I've worked on) for sync logging which as you
point out means a lot of disk thrashing.
> A trick I've done in the very distant past when disk speeds were horrible was
> to create a virtual disk in ram (ramdisk), let the leases file live there and
> once a minute or so, copy the leases file to a persistent disk.
SSDs have got bigger, faster, cheaper over time. Switching to SSDs would make a
huge difference - as long as the whole system supports TRIM and you make sure
there's plenty of free space*.
* TRIM means that the SSD knows when a block is no longer part of a file (so it
can be queued for background erasure), and having a large amount of free space
gives a large buffer of free blocks for the drive to use so minimising the
chance of running out at times of peak activity.
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