high performance open source DHCP solution?

Thu Jul 21 00:17:55 UTC 2011

Good luck buying X25-Es; they're out of production and all gone from
supply chain.  Replacement 710 and 720 models are ETA in late August
at the moment.

Micron has some large-cap SLC drives in the chain for
September/October/ish timeframes.

Ramdisk with rsync or rdiffbackup to spinning storage will do just fine.

-george

On Wed, Jul 20, 2011 at 4:01 PM, Joel Jaeggli <joelja at bogus.com> wrote:
>
> 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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>
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-- 
-george william herbert
george.herbert at gmail.com