Re: high performance open source DHCP solution?

[Owen DeLong <owen () delong com>]

SSDs can be a good alternative these days as well. Some of them have gotten
to be quite fast. Sure, you'll have to replace them more often than spinning media,
but, the write times can be quite a bit better.

Owen

On Jul 20, 2011, at 3:28 PM, Jimmy Hess wrote:

> On Wed, Jul 20, 2011 at 9:31 AM, Nick Colton <ncolton () allophone net> wrote:
> > We were seeing similar issues with low leases, moved the dhcpd.leases file
> > to a ramdisk and went from ~200 leases per second to something like 8,000
> > leases per second.
>
> Yes, blame RFC2131's  requirement that a DHCP server is to ensure that any
> lease is committed to persistent storage, strictly before a DHCP
> server is allowed to
> send the response to the request;   a fully compliant DHCP server with
> sufficient traffic
> is bound by the disk I/O rate  of underlying storage backing its database.
>
> I do not recommend use of a RAMDISK;  it's safer to bend the rule than break it
> entirely;   a safer way is probably to use a storage system on a battery-backed
> NVRAM cache  that you configure to ignore SYNC() and lie to the DHCP server
> application,  allowing the storage system to aggregate the I/O.
>
>
> Of course,  committing to a RAMDISK tricks the DHCP server software.
> The danger is that if your DHCP server suffers an untimely reboot, you
> will have no transactionally safe record of the leases issued, when the
> replacement comes up, or the  DHCP server completes its reboot cycle.
>
> As a result, you can generate conflicting IP address assignments, unless you:
> (a) Have an extremely short max lease duration  (which can increase
> DHCP server load), or
> (b) Have a policy of pinging before assigning an IP, which limits DHCP server
> performance and is not fool proof.
>
> --
> -JH
>
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