We've recently setup ISC DHCPd with failover for lease information, and LDAP as a configuration source (mostly because of our need for dynamically adding dhcp reservations for cable modems, etc) -- we don't have any performance issues thus far, but I'd imagine in a failover environment, it might be safe to consider a ramdisk for leases. Obvoiusly breaks RFC2131, but...
Walter Keen Network Engineer Rainier Connect (P) 360-832-4024 (C) 253-302-0194 On 07/20/2011 03:28 PM, Jimmy Hess wrote: > On Wed, Jul 20, 2011 at 9:31 AM, Nick Colton<ncol...@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 > > _____ > NANOG mailing list > NANOG@nanog.org > https://mailman.nanog.org/mailman/listinfo/nanog _____ NANOG mailing list NANOG@nanog.org https://mailman.nanog.org/mailman/listinfo/nanog
