Cross country point to point link question

Question for someone with some experience with long haul links (Las Vegas -- New Jersey)

[Cisco 4510 - SVI-VLAN x]---trunk---[Nexus5K LH optic]===fiber==={carriers across country}===fiber===[Nexus5K LH optic]---trunk---[Cisco 4510 - SVI-VLAN x]

We have two circuits, one that is the same vendor from east to west, and the other circuit is a two vendor deal. Both circuits are 1 Gbps with around 67-70 ms delay.

As soon as we had the links turned up, our SAN guy started complaining about poor throughput, asking us to throw in a couple of wan accelerators.
He was seeing a max throughput of around ~200 Mbps.

Question: For a long haul 1 Gbps link with 67-70 ms delay, would installing a pair of wan accelerators make a big difference?

-Petter Bruland

Assuming you're doing FCoE or just iSCSI, you REALLY need to make sure your SAN vendor blesses something messing with packet headers on the SAN traffic. I don't think the caching mechanisms on the typical accelerator would help at all either. I somehow doubt they would support that unless they have their own solution.

If you're just doing SMB or NFS or something similar then yes it would probably help overcome performance issues tied to latency quite a bit. But again, the magic is usually all tied to compression, TCP header modification and caching algorithms to local storage on each device.


Hi Petter,

Do you know if your SAN guy has already done the appropriate TCP window
size modifications to fill the pipe up?

Regardless, I am using WAN optimizers to do iSCSI storage replication
across a 230-320 ms 300 Mb shared pipe and have been extremely pleased with
the results. And the compression and caching works great. Of course, YMMV
depending on the nature of the payloads.

I wouldn't go as far as saying you need permission from your storage vendor
to do it, but you should at least ask if the data is encrypted or
compressed during native replication sessions. If yes (and if there is no
way to turn that off), then a WOC won't do you much good at all, as the
only major trick they'd have left is some TCP optimization, which of course
you can mostly do for free.

Feel free to contact me off list if you want to discuss particulars.