RAID for NAS

Just a quick question, I have just purchased a 4 bay NAS that supports RAID 0/1/5/6/5+Spare/JBOD. I was thinking of configuring it as RAID5 but would it be better to configure it with 3 disks in the array plus 1 hot spare or use all 4 disks in the array with no spare?

All disks are 2TB so I understand the 3 disk array will give me 4TB and a 4 disk array will give me 6TB of storage.

Do you need more than 4TB?

Assuming it is a hotswap setup, and the system is mission critical, I would go with the least drives (cost and lesser failure chance, and less power used and heat generated for that matter). If you can put up with downtime, and you want the extra space, get four and order more if it goes down.

If you want space and no downtime, four plus spare.

All about risk and how important your data is.

If you do RAID 5 with one spare, I would imagine when a drive fails, it immediately spins up the spare disk and starts returning the array to a redundant state. You can then remove the failed disk, and bung in another one ready for the same event to happen again.

If you skip the spare, then there will be a period where the array is in a non-redundant state until you replace the failed disk and it rebuilds it again.

Swings and roundabouts. Personally, I would do a RAID 5 setup on a 4 drive NAS. If you had 8 drives, then RAID 6 is another option (you can lose two drives) or even RAID 6 + spare, but with only 4 drives, I would skip the spare option.

I have a 4 bay NAS unit and run in RAID 5 with 4 2TB disks. If 1 drive fails the system will run in a degraded state until the drive is replaced. If 2 disks fail, the data is toast, but I'm okay with that.

Also, you'll actually only have about 5.5TB of available space as your 2TB drive isn't really 2TB..

This is what I was thinking, instead just have a coldspare incase of failure...

Just for simplicity I said 6TB, but it goes without saying that it would actually be a bit less than that