Do I need to rebuild my RAID array in Dell with PERC?

With the DELL Perc controllers, replacing a drive in this manner is normally pretty easy.  Just pop it in and reboot the server.  As long as the OS loads, you'll be all set.  It will rebuild in the background.   Performance will suffer for the time it takes the raid to rebuild but you shouldn't have to do anything.

OK interesting, so how can I confirm that it has rebuilt successfully. When I loaded the new drive (which was a few days after the old drive failed) I had powered down the server, popped the new drive in and rebooted, the OS booted fine, but I noticed that there was no data activity going on on that drive. So I rebooted again so I could go in the BIOS Perc controller and that's where I saw

1. Online A00-00
2. Ready (Newly replaced drive)
3. Online A00-02
4. Online A00-01

Then continued to boot back to the OS. It's been up all day (since 9:00 AM EST) and the data activity light is still not active on the new drive. How would I confirm that the array has been rebuilt? If it hasn't would I then manually rebuild the array with the Open Manager Array utility?

Yes, you're going to have to rebuild the array manually.  
It may just be the age of your Perc or how it's configured.  It should rebuild on it's own.  

I'm assuming that the status in the Array utility is showing as degraded.  If so, boot into the OS, take a good backup. (always the case whenever you do anything, make sure to have a good backup)  and then go and rebuild it.

You're lucky in that the OS loads and you can operate.  You can get a good backup and that proves that the raid is functioning in the manner that it is suppossed to so the rebuild shouldn't be any problem.

Also, check all your drives for bad sectors.  Recent studies have shown that one bad sector increases the odds of the drive failing in the next 30 days by 67%.

I just installed the Open Manager utilities but have not yet been able to reboot...so once that's done then I'll go in and check. I have a backup already so we're good. I just need the database backup to run tonight then I can rebuild. This is all doable with the open manager utility correct?

It looks like your fourth drive was configured as a hotspare therefore when one of your drives failed the hotspare immediately kicked in and the rebuild started. The rebuild probably happened without you noticing. To confirm that your array has been rebuilt check the status of the array... it should state OPTIMAL if the rebuild is complete. If the status is CRITICAL then either the rebuild is still in progress or has not started at all.
Now that you have replaced the faulty drive and its status is ready you have to assign it as a Hotspare. You can do this either through Bios level or your raid management software.

Note. Some people like to keep the order of their drives in the array as it was before but it is not necessary.
That is you now have
1. Online A00-00
2. Hotspare
3. Online A00-02
4. Online A00-01

Instead of
1. Online A00-00
2. Online A00-01
3. Online A00-02
4. Hotspare

Once you are sure that your array is Optimal and the Hotspare has been assigned you can manually (through raid manager) put offline Disk 4. (Online A00-01). This will result in the new Hotspare ( Drive 2. Hotspare) kicking in and a rebuild commences.  Thereafter you should make Drive 4. ready and then assign it as a hotspare.
Then you will have
1. Online A00-00
2. Online A00-01
3. Online A00-02
4. Hotspare

The suggestion of neopad to make your 4th drive hotspare instead of your second implies that during the neccesary rebuild, your system is not fault-tolerant. If at that point another disk fails, you loose everything. This risk is - in my opinion - not worth it.

So then it is best to simply set the new drive as a hot spare and leave it like that?

Neo was correct that the 4th drive was originally a hot spare.

Great thanks, just to be thorough. I do not need to rebuild, in either BIOS or the Array Manager I can just set the drive as a hot spare and that's it.

Whenever a RAID array needs to be rebuild, it will use any available hotspare automatically, without any user intervention.
That's why that's always the only thing you need to do: remove defective drive, insert new one, mark it hotspare.

OK, one last question, I'll probably just do it in BIOS...not being familiar with PERC can someone give me a brief set of instructions on how to set as a hot spare. I was looking around in there earlier and there wasn't anything intuitive about setting it as a hot spare. It's Dell SCSI 320-1 PERC 4/SC

Thanks!

Nevermind, I got it...I was just missing it. F4 makes the drive a "hotspare" I was looking for hot swap (ode to hp/compaq). Any that was it and the array now looks like this

1. Online A00-00
2. hotsp
3. Online A00-02
4. Online A00-01

Thanks for all of your help everyone.