gerhardub
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Network Latency Question: Gigabit Fiber vs Gigabit Copper
Ok,
So I'm in the process of setting up a iSCSI EqualLogic PS300 SAN. The unit uses 6 - Gigabit Ethernet ports (3 on each storage processor card) and comes with the ability to use Gigabit Fiber (1000BaseSX) via SFP or standard 1000BaseT ethernet jacks [SFP slot next to a gigabit jack].
What I'd like to know is:
If you use 1000BaseSX (via SFP modules), will it actually decrease your network latency compared to copper?
My network back bone is a Cisco 4507R with a series of 6 port blades that support either SFP modules (1000BaseSX or LX) or 1000BaseT.
My interest is that I'll be setting up a HPC (High Performance Cluster) and rather than using 10Gig, Infiniband, or Myrnet I'd like to get the best bang for the buck I've already spent.
I'd like a complete and through answer to this question...
So I'm in the process of setting up a iSCSI EqualLogic PS300 SAN. The unit uses 6 - Gigabit Ethernet ports (3 on each storage processor card) and comes with the ability to use Gigabit Fiber (1000BaseSX) via SFP or standard 1000BaseT ethernet jacks [SFP slot next to a gigabit jack].
What I'd like to know is:
If you use 1000BaseSX (via SFP modules), will it actually decrease your network latency compared to copper?
My network back bone is a Cisco 4507R with a series of 6 port blades that support either SFP modules (1000BaseSX or LX) or 1000BaseT.
My interest is that I'll be setting up a HPC (High Performance Cluster) and rather than using 10Gig, Infiniband, or Myrnet I'd like to get the best bang for the buck I've already spent.
I'd like a complete and through answer to this question...
Your switch, or more accurately your switch modules, are the greatest single influence on latency. There was a recent article in Network World about the untold world of switching, and it may actually have been a module for the 4500 that was the lowest latency out there.
pjtemplin - got a link, title, or date on that article?
There is no difference in speed between copper and fiber. Gigabit is gigabit is gigabit. As long as your copper cables meet CAT5e standards, they support Gigagbit. I would use CAT6 just to be safe.
Fiber does give you an electrical buffer and is resistent to Electro Magnetic Interference. For these characteristics it might be a better choice for a cluster.
Fiber does give you an electrical buffer and is resistent to Electro Magnetic Interference. For these characteristics it might be a better choice for a cluster.
Sorry, the mag is already in the circular file, but it was within the past two weeks that it showed up in my mailbox.
Network World - 11.6.06
"LAN switching: The burning questions"
- Which switches are fastest?
Page 12
'Newman says he clocked a Cisco Catalyst 4948 at around 3 microsec at 10G rates, "which is the lowest I've measured", he adds.'
"LAN switching: The burning questions"
- Which switches are fastest?
Page 12
'Newman says he clocked a Cisco Catalyst 4948 at around 3 microsec at 10G rates, "which is the lowest I've measured", he adds.'
ASKER
Ok guys,
To restate my question:
Does fiber gigabit have lower latency than copper gigabit?
Specifically, does multimode fiber plugged into a Cisco 4507 or 6503 using 1000BaseSX-SFP have lower network latency than 1000BaseT?
The "gigbit is gigabit" argument doesn't take into account that possibility that light is faster than then movement of electrons down a copper wire...
When you compare 10G, Myrnet, and Infiniband to COPPER gigabit, you tend to see 5 times higher latency with copper (25ms comapred to 3-6ms).
What I want to know is if anyone actually KNOWS (hard numbers) if there is a difference in latency between fiber gigabit using a SFP and normal 1000BaseT copper?
Thanks.
To restate my question:
Does fiber gigabit have lower latency than copper gigabit?
Specifically, does multimode fiber plugged into a Cisco 4507 or 6503 using 1000BaseSX-SFP have lower network latency than 1000BaseT?
The "gigbit is gigabit" argument doesn't take into account that possibility that light is faster than then movement of electrons down a copper wire...
When you compare 10G, Myrnet, and Infiniband to COPPER gigabit, you tend to see 5 times higher latency with copper (25ms comapred to 3-6ms).
What I want to know is if anyone actually KNOWS (hard numbers) if there is a difference in latency between fiber gigabit using a SFP and normal 1000BaseT copper?
Thanks.
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ASKER
So,
The answer is that the coversion process of electrons to photons and then from photons to electronics slowss things down slightly... and in one of the artices indicates that at full capacity [due to the switch] the difference was 5 times that of copper, with respect to latency.
On a 750Gb backplane like the Cisco units I'd probably not see the 100% utilization that would cause the worst case of 5 times the latency...
The answer is that the coversion process of electrons to photons and then from photons to electronics slowss things down slightly... and in one of the artices indicates that at full capacity [due to the switch] the difference was 5 times that of copper, with respect to latency.
On a 750Gb backplane like the Cisco units I'd probably not see the 100% utilization that would cause the worst case of 5 times the latency...