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New Member

Will WAAS help if we have 15ms latency?

We have 2 sites that have 15ms latency between them over a DS3.  Every day my customer is moving several 2GB compressed files between the sites using a straight CIFS file copy.  Moving a single file takes about 20 minutes currently.  I'm assuming I'd buy WAE-674 appliances at each site plus a CM.

Given 15ms latency and previously compressed files, will WAAS really help that much?  The source files and the compression used I think result in very little duplicative chunks of data.

Can anyone give me a recommendation for how much faster the file tranfers might be?

I'm trying to give my customer some feel for the benefit of spending money on WAAS.

Thank you.

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9 REPLIES
New Member

Re: Will WAAS help if we have 15ms latency?

The compressed content may reduce the effectivness of the WAAS.  Unless your 45Mb DS3 is being heavily utilized, WAAS may not provide a noticeable difference to the end users on that circuit. I would also like to hear from one of the Cisco engineers on this post about how DRE is used when the WAAS is presented with common content that is compressed by the server.

Example of a use case for WAAS connectivity on low latency links:

I have two sites in Brazil that are 12ms apart.  Each has a WAAS. The content was compressed. The branch site has three E1s bonded into a 6Mb IMA group.  One of our LAN administrators was imaging 20+ desktops in the branch office with content pulled from the other Brazil site.  WAAS reduced the load on the 6Mb link by optimizing 40GB of CIFS traffic into a few hundred MB.  The optimization of that traffic was the single largest reduction we had seen.  We actually sent screenshots to the Cisco WAAS business unit we were so impressed.

Check out the screenshot attached below, notice the WAFS reduction at the bottom.

New Member

Re: Will WAAS help if we have 15ms latency?

Hi,

There will not be any major decrease for the latency, regarding what I have seen on my 33 WAASes.

But this files will be cached and only delta will go over the WAN, if it its cached of couse.

Also there will be an fully optimized for the CIFS as CIFS is working very slow, becouse of the MTU and windows size over a WAN without any optimization.

Ryan: Are you running the old WAFS for CIFS?

This not supported in 4.2.x version, also Cisco is recomended to run AO.

I think you known this already, sorry.

Jan

New Member

Re: Will WAAS help if we have 15ms latency?

Actually these boxes are running 4.2.3.  The Central Manager is reporting the traffic as WAFS, even though it is the CIFS AO providing the Acceleration.

New Member

Re: Will WAAS help if we have 15ms latency?

I can see this also now and for me it’s strange as we are not using the old WAFS and only AO.

I apologies for this that I dint look before in CMA.

Cisco Employee

Re: Will WAAS help if we have 15ms latency?

Hello Everyone,

Looking at Tod's question and further details by few more people, few things to consider here.

1. You are transferring a pre-compressed file across WAE and WAN. which means "LZ" compression will not be useful in this case. One option - try transferrign non-compressed file. This might help speed up the transfer as then WAE can apply TCP and DRE optimization in better way to non-compress traffic and compress it too.

2. If you use a pre-compressed file, From WAAS perspective, LZ will not give you any benefits. Further, this might affect the DRE usage / CIFS cache usage for this file, depending on CIFS AO being used or not.

Let me give you an example.

1. Let's take a 100mb pre-compressed file. This file when passes thru WAE, will be cached either in CIFS / DRE cache on disk and then will be applied TCP window / buffer optimization. LZ compression may be applied but will not yield any good result.

2. Now, let's says only 1byte changes for this 100mb precompressed file. Which changes the whole compressed file that comes out due to the inside single byte change and that will result in non-matching delta cache / cifs cache that was already populated in step 1. This further means that DRE / CIFS cache will be of no use and it will generate new cache as the compressed file is changed.

3. On the other side, if you are transferring a non-compressed file, it will only apply new DRE caching to changed byte and not the whole 100mb file.

4. The other option is - you may want to use only TCP / DRE for this one and ignore the LZ because the file is already pre-compressed.

My understanding and experience says - WAAS will do much better with non-compressed file and CIFS AO applied to that file. Otherwise, latency or bandwidth is not an issue here as far as I can say.

Hope this answers your question.


Regards.

Cisco Employee

Re: Will WAAS help if we have 15ms latency?

Further, Ryan got good result for his pre-compressed images as they remain same and does not change frequently. So, it can use DRE / CIFS delta cache from the past.

New Member

Re: Will WAAS help if we have 15ms latency?

The files come to us compressed, so uncompressing is not an option.

When you say "ignore LZ", do you mean I should configure the WAE to not do LZ for one of the TCP sessions? 

Cisco Employee

Re: Will WAAS help if we have 15ms latency?

Yes. Select TFO with DRE option under Policy Action.

Regards.

Cisco Employee

Re: Will WAAS help if we have 15ms latency?

Moreover, as mentioned already you may benefit from TCP Optimization, LZ compression (when data transferred is worth compressing) and some Application Optimizers. You will also observe caching benefits when transferring large files that would usually take more than just a few seconds to transfer on a 15ms latency link. However, for small files, which would transfer very fast over a low latency link, then you may want to avoid any delay added by Hard Disk I/O as it could be noticeable on low latency links (the cached data is saved in the WAAS HDD). For example, if you have an application that runs remotely and you expect it to transfer many small files over a specific TCP port for example, in this case you may want to create a classifier to bypass DRE/CIFS for this specific traffic.

Regards,

Fabio Bergamo
Cisco TAC
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