At 12:51 AM 2/29/00 -0500, Nick Bastin wrote:
>>On Mon, 28 Feb 2000, Nick Bastin wrote:
>>
>>> Exactly. The 7206VXR will still outperform a high end linux system,
>>> because there are other demands on the bandwidth of the PCI bus in your
>>> linux system. Also, it's worth noting that while Cisco classifies the
7200
>>> series in their 'High-End Routers', it's a cheap box intended for
>>> enterprise work. The newer 7576 can push 4Gbps sustained across the
>>> chassis, and even the older 7507/7513 can do 2Gbps. I'm not suggesting
>>> that we'll ever get linux to touch the capabilities of a 12000 (or a
>>> Juniper M20/M40), but PC hardware issues aside, the kernel ought to be
able
>>> to push packets as well as any Cisco 7xxx series router.
The first statement is simply not true. The 7206 doesnt have the CPU to
utilize its supposed additional bus capabilities. A 7206 cant do 2 full T3s
with bandwidth management and a PC can. Cisco will tell not recommend a
7206 for this....
a fully loaded 75xx series can theoretically "do" those numbers, but many
dont understand that the performance is not linear...the numbers comes from
loading all busses under ideal conditions. You will not see much additional
performance until you exceed the pci bus limits of the PC.
[snippage]
>> What other demands? A Linux based router is running a bunch
>>of cards, not disks/etc.
>
>Well, on most of my firewalls/routers, I have a PCI video card. It might
>not be doing much, but it's still sucking up some bus bandwidth. Also, if
>I'm running disk at all for some reason, the IDE controller is on my PCI
>bus too. I tend to run disk on the firewalls, and not on the routers,
>although that's mostly a semantic distinction (the firewalls do logging,
>the routers don't, although I could do this over the network too...)
The amount of PCI bus bandwidth used by a video card in text mode and an
IDE used for logging only is inconsequential. You certainly want to keep
your disk usage at a minimum...and make sure you do your backups
(incremental of course) during non-peak times.
The "trick" with a PC with a single bus is to minimize the number of
devices, because each additional device on the bus increases the
"contention" formula for the bus, thus increasing the chance for underruns
and overruns due to a bus master not being able to get the bus in time. One
loaded full-duplex ethernet card is much better than 2 half-loaded
cards....when building a high-performance pc router you want to mimimize
the number of cards and front end the box with a switch rather than load
the box with cards.
Multiple PCI busses is the cure for this...coming soon to a theatre near
you.....
DB
Emerging Technologies, Inc.
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