expected disk throughput

bit depth and sample rate help with this calculation. It depends on your drives.

I tend to have trouble with a single 7200 RPM drive with a 32 MB cache hard drive when recording 10 tracks at 24 bit 96kHz.

I don't have the same ceiling when I record them as a single file.

For play back I can handle more than that.

When recording in a single file, I can record 10 tracks 24 bit 96kHz on my little laptop hard drive with an 8 MB cache. I record to a single file using the tools that came with my audio interface, but then I'm not working in sonar, just capturing a field recording.

If you get a second drive, you might want to stripe it with the first (Raid 0). I use an icy dock

http://www.icydock.com/index.php

Mine holds two drives of the same size and you can hardware stripe them, giving you close to double the speed of the single drive. It's pretty cool but it isn't silent.

Practical limit of 96K 24 bit mono tracks. 
USB 2.0 = 107 Mono tracks 
SATA/300 = 230 mono tracks 
- Bob Katz - Mastering Audio the art and science - p 309 
 
Keep in mind that if you drop to 44.1 kHz, you're still recording a ton of great sound and now you can record twice as much!
 
Additionally, check preferences > File > Audio Data. I tend to keep my record and render bit depths at 24. Sometimes I let my render go to 32 if I'm doing small projects. It's good to be aware of these settings. If you have a 24 bit interface, but you are recording at 32 bit, you are writing 32 bit files with a lot of 0s at the end. :-)
 
Does someone out there foresee a 64bit interface? I don't know... it's an option in the drop down.
 
Lastly, for big projects I tend to use 44.1 even if I record the tracks a few at a time and the reason is this... If I record at 88.2 or 96, then bouncing to stems takes longer. Also, my processor runs hotter and I'm more likely to experience audio glitches.
Overloud's TH2 can get a little glitch when the processor is worked hard (and TH2 pushes the processor). I end up applying the TH2 or freezing the track if I have more than 4 instances of TH2 on a 24 bit 96 kHz project in order to free up resources. 44.1 kHz use substantially fewer resources.

I used a couple soft synths but they're frozen.  For samples, just EZ Drummer.  I don't believe I'm doing anything particularly stressful, just trying to get a generic box to do 22 tracks.

I'll spend some time submixing tomorrow so I have less running tracks.

CAF

@Bristol_Jonesey Thanks for the thumbs up.

@Chewing -- It took me more than a few projects to begin to get a grip of the constraints that were my lowest ceilings. Take your time and and keep questioning what you think you know.

And keep posting questions with as much clarity as you can spare. Many good trouble-shooters lurk in these halls. If you give them what they need, they can help you improve your setup.

You should consider Deferred Procedure Calls as well. I use a tool that was free called Latency Monitor

http://download.cnet.com/LatencyMon/3000-2086_4-75300293.html

This tool can help you identify if your drop outs are actually being caused by a some bad behaving driver that only fires once every 20 minutes and then when your energy saving software checks your USB ports to see if they are in use.

You can find the particular bad boy I'm talking about under Advanced Power Settings >  USB Settings > USB Selective Settings > (Ensure this is disabled when you are recording).

For me, I also disable my WIFI card, web cam and Microsoft ACPI Compliant Control Method Battery. For you, the items causing DPC issues may be different. And, indeed, your problem may be entirely related to your drive.

I also had a lesson regarding virus scanning. Usually, Virus Scanning wasn't a constraint for me, but one day I was recording 10 tracks at a time in a live scenario where all the tracks were an hour long. I hit stop and record quickly to write the files and then keep the tape rolling, but the problem was the virus scanner immediately kicked into full gear scanning the tracks. This wouldn't have been a problem if there weren't 10 huge files to scan while concurrently writing to the same disk being scanned.

Now, I disable virus scanning and windows updates before working. Sometimes, they are off so much that I instead turn them on when I'm not working. You shouldn't have to disable all Virus Scanning, but set your Sonar Folders for exclusion from scanning. 


And watch out for the Anit-Malware tool after installing new software. After a new software install, it will scan all the software when it thinks you aren't busy with your computer (judged by how often you're tapping your keyboard).