I was eq`ing a kick track and noticed it was:(KickMic.wav 3884).
that's a lot of wavs in 2 years and I`m wondering if it is time to replace my C Drive(Program drive) before it wears out.
It is one of 3 WD 1TB drives in the box and I thoroughly backup with Acronis and external drives but,I am wondering what is the shelf life of a hard drive and whether its worth 99 bucks to ensure another 2 years of hard work-the last drive failure I had 2years ago was an absolute PITA to restore and although successful was not worth 99 bucks!
cheers
tony   

I don't know what the "MTBF" is on your hard drive(s).  I have drives that are over 6 years old and still working without problems or errors.  However, as a conventional hard drive is an electronic/mechanical device it can fail anytime (reason for backups).  I don't replace drives as a routine PM item. 
 
 

Since you have 3 drives and use externals as well, no, I wouldn't worry about replacing the drive until it failed.
 
Keep the backups current and let it roll.... or spin, as the case may be.
 
Only if it starts acting flaky and or develops noise would I consider a preemptive replacement.

In fact, the best insurance against drive failure is a backup (image even better), and the next best is a drive that has been running fine for six months or more. There is a high rate of failure in new drives. After that shakedown cruise period that weeds out the drives with defects of construction, the failure rate levels off.
If you have backups, and want to spend the money on insurance you could buy a new drive and put it on the shelf. Old drive (any of your three) fails, you can swap in the new drive, restore the failed drive image and be back to normal running in a half hour.
 
Given that drive prices tend to fall over time, the drive on a shelf will probably cost you more than waiting to buy one when one of your drives fail. But if you have to pay top retail at a local shop to do a quick replacement, you will probably do better buying one on sale and on line before the failure occurs (if it ever does before you scrap the machine).
 
https://www.usenix.org/legacy/events/fast07/tech/schroeder/schroeder.pdf

thanks for the advice!

I had a WD drive that failed. None of the other ones have and are Seagates. Anyway, a harddrive should probably last about 10 years but they do not.
My old computer's drive is going on 7 years old, but a newer one was put in about half that time back then.
 

I've had the unfortunate circumstance of having an external backup drive go bad just when I needed it for a recovery, so I advocate for multiple backup drives.  I don't keep them all 100% current, but all of them are relatively recent in case I have a calamity again where my main drive goes out and then the backup isn't working, at least I'll have at least one or more additional backups in the wings.

I alternate between two "backup" hard drives.  That way, as noted, if "Murphy's Law" strikes I still have a fairly recent backup. 

I recently had to upgrade my C drive. It only took about 15 minutes using Paragons Software to copy an OS from one drive to another. It copied the whole C drive to my D drive, I removed the old C drive and rebooted and it just ran perfectly.
If you've flogged your hard drives for a couple of years then for $99 it's a small price to ensure another couple of trouble free years. Better to do it in a control situation than wait for it to go poof. I've done that in the past too, backup drive also failed and it cost me $500 for a data recovery company to get all my data back for me.

Lesson learned.

I used to have a routine of every 2 years I would  buy a new ( usually bigger) hard drive , pull the old one and either put it in a drive encloser as a back up or move it down to become drive E.
I have become lazy I guess and now have a C drive that is 5 years old and the E drive is a little bit older. My external drive must be 4 years old but is only turned on briefly to run a back up.  
I think its time I replace my C drive and buy another external. I don't like the idea of Murphy's Law killing all 3 in one day because of a power surge or acts of God. 
I especially don't like the idea of loosing my last 4 years of work. 1,000 of hours ---poof!