Best practice for replacing dying hard drives in a NAS

[AJFILMS]

I currently have a NAS as backup for all of the data in my Laptop and Desktop. My laptop has 2 drives in RAID 1 so I'm less concerned about losing data from it. However my Desktop has a ton of miscellaneous drives from throughout the ages with no redundancies other then me having backups of my important data on my NAS. The NAS currently has 4 Dell Enterprise drives in RAID 5  and they are at the end of their lives. I don't know exactly how old they are, but they are at least 6 years old. I was already planning on replacing every drive in the NAS, originally planning on buying the first new drive 6 months from now then adding a new one every 6 months until all the drives are new. I also then planned on replacing the oldest drive either every 3 years or every 5 years from that point. Unfortunately last night 1 of the drives in my NAS died, out of concern about losing data I've shut down the NAS until my new drive arrives on Monday. I don't have the money to replace all of the drives right now, but I was thinking about buying a second new drive which brings me here. Would it be better practice to replace a second one of the 6 year old drives now or wait until a second drive dies and replace it with a second new drive already on hand. Basically I already plan on buying a second hard drive, but I'm not sure if I should install it right away or wait until a new drive dies.

[leadeater]

5-7 years is a pretty typical time frame for drives to start dying.  So the big thing to watch out for is when you are rebuilding the array when a drive is replaced, swapped or failed, the load on the remaining disks can be quite high for a long time which could cause more to fail. This is usually quite a low risk event however the older the disks the more likely.

 

What is the total usable capacity of the NAS and what is the size of the new disk you have?

[AJFILMS]

3 minutes ago, leadeater said:

5-7 years is a pretty typical time frame for drives to start dying.  So the big thing to watch out for is when you are rebuilding the array when a drive is replaced, swapped or failed, the load on the remaining disks can be quite high for a long time which could cause more to fail. This is usually quite a low risk event however the older the disks the more likely.

 

What is the total usable capacity of the NAS and what is the size of the new disk you have?

The current drives in the NAS are 8tb each and are pretty much full, the new drive I just purchased is 12tb just so that when I've replaced all the drives I can expand capacity

[leadeater]

3 minutes ago, AJFILMS said:

The current drives in the NAS are 8tb each and are pretty much full, the new drive I just purchased is 12tb just so that when I've replaced all the drives I can expand capacity

Hmm, well scratch that suggestion I was going to make.

 

If money wasn't a factor I would say replace more drivers sooner than later but that's not realistic. If the current rebuild goes fine then I'd say 3-6 more months should be fine.

[AJFILMS]

15 minutes ago, leadeater said:

Hmm, well scratch that suggestion I was going to make.

 

If money wasn't a factor I would say replace more drivers sooner than later but that's not realistic. If the current rebuild goes fine then I'd say 3-6 more months should be fine.

I currently plan on picking up 2 new drives now. One to replace the dead drive, and the second I'm not sure what would be best to do with. If I should install the second drive after the first drive is rebuilt or wait until a second drive dies to replace it or until I have enough drives to fully replace the array. My thought is if I wait till a second drive fails then I would be replacing the next drive likely to fail. Whereas by replacing a random drive the new drive that drive might not be the next drive to fail.