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high performance open source DHCP solution?



On Jul 20, 2011, at 3:37 PM, Walter Keen wrote:

> 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...

Use an ssd, all the cool kids with monolithic databases and tpc-c style workloads are doing it and since your storage requirements are negligible it ought to be fairly cheap.

http://www.intel.com/design/flash/nand/extreme/index.htm

Bandwidth Sustained sequential read: up to 250 MB/s
Sustained sequential write: up to 170 MB/s 
Read latency 75 microseconds I/O Per Second (IOPS) 
Random 4KB Reads: >35,000 IOPS
Random 4KB Writes: >3,300 IOP

and that's for just one disk.

> 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<ncolton at 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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