Re: [EXTERNAL] Re: extremely slow DHCPD startup time

This wouldn't happen to be on a virtual would it?  

In my somewhat limited experience (only a couple high traffic DHCP servers in virtuals - many on single SSD storage systems), I/O is a problem for DHCP servers installed in virtual infrastructure (no matter what sort of storage you have on the back end). A single CPU - multi core Xeon 1U system with a single SSD and 16GB RAM will run circles around virtuals for ISC DHCP in the I/O department.  No idea why.

----- Original Message -----
> From: "Shane Merritt" <[email protected]>
> To: "Users of ISC DHCP" <[email protected]>
> Sent: Thursday, August 4, 2022 4:18:04 PM
> Subject: Re: [EXTERNAL] Re: extremely slow DHCPD startup time

> The server disks are already SSD. The total max available lease space according
> to dhcpd-pools is 283,751. I did a restart on one of the pair earlier and the
> time was about 10 minutes, but activity is low at the moment since fall
> semester hasn’t begun.

> Shane Merritt

> Office of Information Technology
> The University of Alabama
> [email protected]

> From: dhcp-users <[email protected]> on behalf of Sten Carlsen
> <[email protected]>
> Date: Thursday, August 4, 2022 at 2:54 PM
> To: Users of ISC DHCP <[email protected]>
> Subject: [EXTERNAL] Re: extremely slow DHCPD startup time

>> On 4 Aug 2022, at 21.05, Greg Sloop < [ mailto:[email protected] | [email protected]
>> ] > < [ mailto:[email protected] | [email protected] ] > wrote:

>> I'm sure others will have some useful suggestions - but I do know that improving
>> disk I/O can seriously improve performance.

>> I'm not sure if that will improve restart/start/reload times.

>> It would be pretty easy to test though, say swapping for an SSD/Nvme.

>> (Or if you like living dangerously, putting the disk in RAM.)

>> On Thu, Aug 4, 2022 at 12:02 PM Shane Merritt < [ mailto:[email protected] |
>> [email protected] ] > wrote:

>>> I have a failover pair of DHCP servers running 4.4.2-P1 that handle a DHCP for a
>>> very large wireless network (>75k devices active at any time). The leases file
>>> on these boxes is around 200 megabytes. The problem I am having is when I need
>>> to make a change and restart, DHCPD takes over 25 minutes to start giving out
>>> addresses. I assume this is due to the large lease file. I see that there are
>>> tons of leases in the file that are “binding state free” that in some cases are
>>> months old. Are there any suggestions to improve this situation?

> AFAIK the server will fill its internal tables with every possible lease, most
> of them empty or marked free. I could be wrong about this.

> So the question is how large your net blocks are?

> If you e.g. have a /8 address space, that would amount to the server having to
> populate 2^24 (16 mill) entries in its internal table and do what ever
> processing etc it does for each entry. This may take time.

>>> Shane Merritt

>>> Office of Information Technology
>>> The University of Alabama
>>> [ mailto:[email protected] | [email protected] ]

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