Rob[atSound-Rehab]
Having issues with large projects @96 KHz I'm considering going "all in" on SSDs.

Are you just assuming it's a disk throughput issue with your standard HDD's?
 
If they are 7200RPM and running SATA revision 3.0 (6 Gbit/s, 600 MB/s), or even SATA revision 2.0 (3 Gbit/s, 300 MB/s), you should be able to run many audio tracks.  But that's just the theoretical upper limit of the interface.
 
So here are some real world HDD throughput charts:
http://www.tomshardware.com/charts/hdd-charts-2013/-01-Read-Throughput-Average-h2benchw-3.16,2901.html
 
Based on this info provided by Sweetwater, 1 mono track of 24/96 audio needs 16.4MB per minute.  That's .273MB per second.
http://www.sweetwater.com/sweetcare/articles/calculating-hard-disk-space-required-for-digital-audio-recording/
 
Have you tried running a disk benchmark like this free one, to see what your HDD read/write performance is now?
http://crystalmark.info/software/CrystalDiskMark/index-e.html

abacab

Rob[atSound-Rehab]
Having issues with large projects @96 KHz I'm considering going "all in" on SSDs.

Are you just assuming it's a disk throughput issue with your standard HDD's?
 

 
 
Well, I do get occasional crackles, sometimes only a few, sometimes an annoying lot. And I haven't figured out yet what's causing it; disk performance is one of the possibilities (the others being USB connection, audio driver, Sonar itself) ...
 
I did a lot of high track count recording lately (22-24 mono channels @ 96 kHz) and it worked fine when recording, although I quickly had to realize that I can only do 3 takes in the same place (i.e. Sonar seems to read back the recorded takes while recording the new one, thus reaching some limit) ... when recording into an empty project space it always worked (which sort of rules out USB connection and audio driver).
 
In the most recent tracking session we recorded 7 full songs (22 tracks @ 96 kHz) and it all worked, but there were 2 weird things: the first takes were all corrupted, we rebooted the DAW and it worked fine for the next two 8 hour tracking sessions, all recordings were fine, BUT then again last 3 takes corrupted. very strange. nothing in the windows system logs. thus I suspect the HD ...
 
When playing back these recordings (3-4 take lanes of 22 tracks @ 96 kHz) windows taskmanager shows disk usage at 100% (although it should only be needing 19 - 25 MB/s); reported speed in the task manager is only 60 MB/s, which is at the bottom of your list ...
 

Rob[atSound-Rehab]

abacab

Rob[atSound-Rehab]
Having issues with large projects @96 KHz I'm considering going "all in" on SSDs.

Are you just assuming it's a disk throughput issue with your standard HDD's?
 

 
 
Well, I do get occasional crackles, sometimes only a few, sometimes an annoying lot. And I haven't figured out yet what's causing it; disk performance is one of the possibilities (the others being USB connection, audio driver, Sonar itself) ...
 
I did a lot of high track count recording lately (22-24 mono channels @ 96 kHz) and it worked fine when recording, although I quickly had to realize that I can only do 3 takes in the same place (i.e. Sonar seems to read back the recorded takes while recording the new one, thus reaching some limit) ... when recording into an empty project space it always worked (which sort of rules out USB connection and audio driver).
 
In the most recent tracking session we recorded 7 full songs (22 tracks @ 96 kHz) and it all worked, but there were 2 weird things: the first takes were all corrupted, we rebooted the DAW and it worked fine for the next two 8 hour tracking sessions, all recordings were fine, BUT then again last 3 takes corrupted. very strange. nothing in the windows system logs. thus I suspect the HD ...
 
When playing back these recordings (3-4 take lanes of 22 tracks @ 96 kHz) windows taskmanager shows disk usage at 100% (although it should only be needing 19 - 25 MB/s); reported speed in the task manager is only 60 MB/s, which is at the bottom of your list ...
 

Even if you are running 88 tracks @ 96, it seems that the most that would require is 24 MB/s.  I see that your ASUS MB is SATA 6 GB/s equipped, so no possibility of bottlenecking there.  Your physical disk WD SATA should be the limiting factor of at least 100 MB/s. 
 
The fact that Windows shows 100% disk usage is troubling.  Something else is going on.  Might be time to see what processes are accessing the disk, and perhaps disable some that don't need to be running.

Run Ccleaner and Malwarebytes. After that see how full your drives are. If really full, you may be getting bogged down with swap files. Same goes for fragmentation.

Windows TM disk percentage isn't how much of the available throughput is being used, it's how much time processes are spending "accessing" the disk.
 
 

Thinking about this I'd be inclined to run latencymon for an extended period before pointing the finger of blame at the drive. All kinds of things can cause crackling and dropouts and a SATA 6 interface and fast HDD should be able to shift an awful lot of data without problems.

As well as running latencymon and malwarebytes etc. take a look at the Windows logs. A lot of paging errors or retries at accessing the disk might point to the drive or SATA interface being the problem.

Another possibility is that the drive is getting full, or if partitioned the audio is being saved to the slowest part of the drive. HDDs rotate at a constant speed, which means the outside of the disk passes through the heads at a greater rate than the inner area. Which means data is written/read faster towards the outer edge. An old trick for optimising disk throughput for audio was to partition a drive then use the first partition created (which Windows would place at the outer edge of the drive) for audio. Speed testing a drive partitioned like that would show considerably higher throughput for the outer partition than the inner. Faster drives with more cache and SATA have made that less of a problem and SSDs eliminate it altogether, but it might be worth considering if drive throughput really is the issue here.

FWIW, I bought the 750Gb Crucial MX300 on Black Friday and after culling my 1TB hard drive down to around 500GB by moving stuff off to a 1TB USB I use for backups, I cloned using Acronis as the licence is provided with the SSD. I am running Win10 1st Anniversary plus recent updates 64bit. First time I did it, it failed but that was because what they forget to tell you is after cloning, disconnect your current hard drive (moving the boot order in the BIOS doesn't cut it). Also It is a good idea I gather to connect your new SSD to the same sata port on the motherboard that the old hard drive used. Not sure if it does anything but hey it worked.  Once you are up and running OK, you can shut down, connect the old hard drive to another sata port and it should come back with the SSD as the OS disk as it is first in the boot order. I now use my old 1TB hard drive for audio files and sample files.
Things to note:
If things go wrong with the SSD when you clone, You can download Crucial Storage executive client. This has the facility to clear your SSD so you can try again. The other thing is don't forget to disable any defrag automatic schedules as you don't want to defrag the SSD (they don't like it I gather).
Although Sonar works, IK stuff and Izotope stuff needs to be re-authorised. There may be more.
For me Kontakt etc. was fine, Waves was fine, Ilok licence manager was fine.
Works a treat with Sonar on the SSD and Cakewalk projects on the old hard drive.
I did also splash out on an over the top 8GB RX480 graphics card to lighten the load on my CPU.
My system flies compared to before. Windows boot in less than 60 seconds and Sonar load times are also quicker

BobF
Windows TM disk percentage isn't how much of the available throughput is being used, it's how much time processes are spending "accessing" the disk.
 
 

I would still be concerned about 100% disk active time ... anytime my system gets sluggish and I see something running on a disk at 100% active time, it's trouble!
 
I do like how the new improved Win 8/10 Task Manager also shows the disk throughput for each drive.  Click on the performance tab and then click on the disk in question.  A nice real-time graph at the bottom displays the throughput rate in KB/s, MB/s, or GB/s, depending on the scale of operation.  The stats at the bottom even break out the read/write throughput speeds.
 
However, Windows Resource Monitor (Win 7/8/10) is an even better window than Task Manager into what's going on inside the computer, including which processes are actually accessing each drive, and the folder/file in use.   Here's a good overview: http://www.digitalcitizen.life/how-use-resource-monitor-windows-7

Thanks for all your input and suggestions!
I did some benchmark tests last night and now it's clear that it's not an HDD issue. Read/write speed is about 110-120 MB/s for sequential access on the audio drive (it's a ridiculous 2 MB/s from 4K random access but I believe that does not count for audio recording and playback). 
 
The trouble making project lists about 15 MB/s in the task manager at peak reading times. So disk throughput cannot be an issue. Additionally, I found enough space on the somewhat faster system drive to move the project there for a test. Same audio glitching issues.
 
As I no longer believe this is an HDD performance issue, I started a new thread here (in case you find time to think about this and give your input).
 

forgot to mention, if you have Sonarworks, this also needs re-authorizing if there are hardware changes