Hi vx2 welcome to the forums!
While I stopped using Seagate Drives almost a year ago and switched to Western Digital and more recently I purchased some a couple Hitachi 2 TB drives along with a 2 TB WD Drive.
The WD Green Drives which have been reported to work well in the MSS's are the ones with EADS in the Model Number. The other WD Green Drives have been reported to have issues in the server, not that they are bad but they just cause issues. So even some WD Drives are not a perfect solution.
While its a fact of life, all hard drives will die at some point. They are mechanical and over time they get worn out, its just a matter of when. My last Seagate drive died within 3 months and that particular model was plagued with issues just too bad I was not aware of the issues or I would of avoided the drive.
As for changing the system drive out.....I would check your model number out first to see if it requires a firmware update and to see if others experienced failures with that particular drive.
The recovery process for the EX49x is not as simple as it was with the EX47x and EX48x models and people have reported issues with performing a server recovery using HP's process. All is not lost tho because many good people have worked on finding a solution to this problem and there are posts about it here on this site and 2 come to mind.
Before I continue I recommend you read through this thread to better understand what issues you may encounter with the EX49x recovery process and some people have posted some solutions in there as well. Click on the Link below for more information:viewtopic.php?f=25&t=6307
The first method is to clone the actual System Drive but in doing so you will have to edit a few things but this is by far the best and more simpler approach to changing out your system drive so click on the link below to information on how to Clone your System Drive;http://www.mediasmartserver.net/2010/01 ... tem-drive/
The next process is a little more envolved but you can read about it in the link below:http://mediasmartpodcast.blogspot.com/2 ... sb_09.html
I hope I have provided you with enough information to review to help you better understand the issues you may encouter with changing out the system drive. Once you pick one of the options to do so it will be good practice for you should you need to change the System Drive in the future. I also hope that you are able to determine if your Seagate drive is one with a problem or not and which WD Green Drive you should purchase.
If you should need additional help or information please do not hesitate to ask again and before you begin if you do not have backups of your users and client backups there is a FREE Add-In available on this site developed by Alex (The Site Owner) called BDBB that will allow you to backup your User Information and Client Backups. Its an outstanding program and I recommend it to everyone especially ones who are about to perform a Server Recovery be it just a Server Recovery or a Server Factory Recovery as it will allow you to restore your Users and Client Backups should the need arise. I use it and have restored my Users and Client Backups and it worked perfectly.
Good Luck with changing your system drive! Let us know how you make out.