Hello all,
     I know there are other threads pertaining to this topic, but I didn't want to hijack, so I started this one.  My system specs are in my footer, and I'm using a Focusrite 2i2 audio interface with ASIO drivers. When I go to Preferences/Driver Settings, in the Mixing Latency section, the Buffer Size slider is greyed out, so I click the ASIO Panel button (which for some reason I have to click twice before it opens).  This brings up a very barebones Focusrite ASIO Driver box containing a Buffer Length slider which I have set to 7 msec.  This gives me an Input Latency of 15.3 msec, 676 samples and an Output Latency of 22.3 msec, 985 samples for a Total Roundtrip of 37.7 msec, 1661 samples.  The only way I can get the Total Roundtrip below 10 msec is to set the Buffer Length slider to 1 msec.  To me, a Total Roundtrip of 37.7 msec seems way too high, but maybe I'm using a wrong Buffer Length?  I want to get my Total Roundtrip below 10 msec before I start using a MIDI keyboard to trigger softsynths, or use any amp sims in realtime, and I feel like a Buffer Length of 1 msec is way too low.  FWIW, my buffer sizes in the Sync and Caching tab are set to 512.
     Any thoughts or suggestions, or does this all sound perfectly acceptable?  Thanks in advance!

Hmmm, I just googled "setting asio latency with scarlett 2i2" and got hits from every DAW forum there is and none from the Focusrite site.
 
First "stab in the dark" attempt on my part - Do you have ASIO4ALL drivers installed? If so, you may try uninstalling those as they may potentially conflict on you. Be sure you are running Focusrite's ASIO drivers as well.
 
The best response seen so far was from a Focusrite rep on Gearslutz. Actually that link stinks because the rest of the thread is missing (http://www.gearslutz.com/board/low-end-theory/673185-focusrite-scarlett-2i2-problem-help-me-out.html).

The numbers on the slider are just numbers not milliseconds. They just indicate a relative increase or decrease of in latency.

that's right, the slider defaults to 10 and that's what they recommend. 
There is confusion with latency and it is known that those figures are not what you are going to actually experience. 
Download this and test your RTL it will give you the correct amount, It will be around 5ms with most modern, well oiled computers and  Scarlett. You have to patch your output to your input and make sure to turn off input echo.
 
https://centrance.com/downloads/ltu/

What Sample Rate are you using with your interface?
 
And, for whatever the worth, my input latency and output latency for my Presonus AudioBox 1818 VSL are each 4.7 milliseconds (224 samples), and the total roundtrip latency is 9.3 milliseconds (448 samples).  
 
To achieve that, I have a Sample Rate of 48 k, and an ASIO Buffer Size of 128.
 
You might also consider trying a Sample Rate of 44.1 k, just to see if that also removes this issue.  Make sure the sample rates match, between the interface and Sonar.
 
Bob Bone

Thanks for the replies, everyone. Definitely gave me some things to look at. Unfortunately, I needed to head out of town at the last minute, so I won't be back at my system until tomorrow. I'll try out a few of these suggestions and report back as soon as I can. Thanks again!

The posts above are accurate. When I finally found pictures with screenshots of that ASIO panel it became more clear. There were a lot of posts saying "I have buffer set at 0ms, but see latency of Y milliseconds," so please consider those "numbers" as guidelines (not values). The values listed at the bottom of Preferences->Audio->Driver Settings within X3 are the accurate system latency.

Ok, got back to my system and played around a bit...
 
I hooked up a MIDI interface and attached an old Roland keyboard controller (don't yet have a USB keyboard controller).  Had no MIDI problems and was able to trigger TruePianos right away.  With a Total Roundtrip of 37.7 (according to Sonar), the latency was BARELY noticeable.  I certainly could have dealt with it.  I lowered the Buffer Length slider in the ASIO panel to 4 msec, which corresponds to an Input Latency of 9.3 msec, Output Latency of 13.4, Total Roundtrip of 22.7.  I'm not noticing any latency whatsoever between the time I strike the keys and the time I hear the sound.  Instantaneous. 
I'm curious about the numbers on the Buffer Length slider in the ASIO panel.  It does refer to the number (ranging from 1-20) in msec.  It is called the "Buffer Size" slider in the Preferences/Driver Settings window, but it reflects the number I set in the ASIO Panel, also in msec.  Not sure if having such a low value will cause problems later, perhaps when I have more tracks or plugins running than I do in the current test project.
Aside from triggering softsynths and realtime Amp Simulation (which I have no idea how to set up yet), where else could latency rear its ugly head?  Or is that pretty much it?
 
I appreciate all of your help!

Latency is only an issue when relying on monitoring through the DAW while recording. During playback only, latency is not an issue. This is fortunate as some plug-ins designed for mixing and mastering add significant amounts of latency. It may also be necessary to increase the number of buffers used by the interface to reduce the CPU load during the mixing process.

Like I said, those numbers shown in Sonar are confusing and do not always represent your actual latency. As example my Tascam interface has about the same high numbers as you are showing but if I run the Centrance RTL test, I get that mine is 9 to 12 depending on other settings. 
 
Simple test is turn on input echo with an audio track armed and a guitar plugged in, you'll hear the delay. 
 
And this latency figure has nothing to do with triggering a midi soft synths. That will be instantaneous for almost all interfaces unless you are running a bunch of heavy CPU efxs. It is recommended to bypass all efx bins while tracking both midi and audio. 
 
As Steve has said, pour latency only will bother you if you try and monitor at the output of your DAW while tracking, that is why all interfaces have input or zero latency monitoring. 
Sonar adjusts for playback latency so your new tracks will ( should) be perfectly in sync with the originals. Poorly written drivers, like with Creative Labs, will have issues with sync.