What is ws-x6748-ge-tx fastest datatransfer configuration?

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Jul 21st, 2009
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Hello, I have a 6509 with 2 X sup 720's and 3 x ws-x6748-ge-tx. Our server team has 3 Data Domain backup servers that move Hundreds of gig's of data between them each day. Redundancy is not required. Where would I plug these in for the very fastest data transfer, all three on the same module right next to eachother or all three on the same module but in different channels or spread them across three different modules.

Thanks in advance.


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Roman Rodichev Tue, 07/21/2009 - 22:28
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bandwidth vs. latency

It doesn't sound like a latency sensitive app. You are just concerned with bandwidth throughput. In this case, it doesn't really matter where you connect your servers. 6748 is pretty much line rate with a 40GB backplane access. I would just connect them to the same module same channel. If DFC card is not installed, 6748 will do a header lookup from SUP's PFC3 card, but that's just adding short latency, you are still getting full bandwidth.

By the way, if you are not getting enough throughput for your data transfers, you might want to increase TCP window size on your servers.

Joseph W. Doherty Fri, 07/24/2009 - 16:31
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If you haven't already seen it, you might find this of interest: http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html

From this document, we see that a 6748 has 4 ASICs that control 12 ports, and 2 20 Gbps fabric connections. It's unclear whether there's advanage of keeping communication host pairs on same ASIC or same line card.

Otherwise, for maximum performance, you'll not want any non-fabric cards in chassis with your fabric cards unless latter also have DFCs.

You'll want to avoid oversubscribing fabric bandwidth channels (believe that can be done by only using 20 of 24 ports splitting 48 in halfs for 6748s).

You'll want to use DFCs if the 30 Mpps sup720 isn't enough. (NB: 30 Mpps is good for about 10 Gbps, duplex, but that's also for minimum size packets. Referenced document says 30 Mpps is independent of packet sizes, so up to about 180 Gbps for 1500 byte packets.)

Robert Rowland III Tue, 09/08/2009 - 04:10
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If you create a port channel on sequential ports on a 6748 you get some sort of error/warning message indicating that the max bandwidth is less that "X".

You want to create the PCs so they are something like GI1/1,GI1/13,GI1/25, ....

Joseph W. Doherty Tue, 09/08/2009 - 07:28
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That's interesting. Just to confirm, this on a 6748 card?

a12288 Mon, 07/27/2009 - 05:56
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You should enable TOE on DD side, and enable end-2-end Jumbo Frame support on DD and Cisco, that should boost your overall backup performance.



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