Why two drives for redundancy rather than one drive in the NAS and an external backup drive?

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Why two drives for redundancy rather than one drive in the NAS and an external backup drive?

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DS1522+, E10G22-T1-Mini RJ45 10G Ethernet Module
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Hi, I am setting up the NAS and installing DSM. I have one Seagate 8TB HDD. In the future, I may buy one more to use SHR but not sure yet as I may end up using SSD. Given that redundancy is not the same as backup, what is the point for putting two drives in the NAS vs. one drive in the NAS and have an external drive to back it up? What are the pros and cons of each approach? Perhaps just a possible slight increase in speed depending on the RAID type? What else? I probably won't use more than 4TB in the next 1-2 years.
 
SHR/Raid is not an backup, it's only availability of the data. If you use SHR/Raid1 you also need an external backup. The advantage of SHR/Raid is, if one HDD fails, your system is still running and available, you just need to replace the broken HDD and start the repair of your SHR/Raid.
Edit: What DS are you using?
 
I am using DS1522+. My idea is that the entire NAS could fail so if I put two drives in it, they could all die together. However, if I put only one drive in the NAS and buy an external drive as a backup for the NAS, isn't that better than redundancy?
 
isn't that better than redundancy?
You can’t compare backup with raid. As it was already said raid is not backup. So it comes down to what you need/want.

You should always have a backup of your data or your irreplaceable one at least. With raid you get redundancy and service uptime as well as data access even if the drive has died (depending on the configuration).

So if you can live with downtime, you don’t need redundancy/raid, but you should have a backup regardless.
 
As already said, the RAID configurations that include redundancy provide you with continued system (and data) availability in the event of drive failure. There are some RAID configurations that just provide increased storage that spans the drives, and you get little to no data protection if a drive fails.

There's no rule that says you have to use the types that have redundancy, that's your choice and data and your money and your time. You've got five bays and you can populate them as best suits you. If you think you might want to add redundancy to a storage pool at a later date then start a single drive SHR (with no drive protection). If you are sure you won't need it then a Basic storage pool will do.
 
As already said, the RAID configurations that include redundancy provide you with continued system (and data) availability in the event of drive failure. There are some RAID configurations that just provide increased storage that spans the drives, and you get little to no data protection if a drive fails.

There's no rule that says you have to use the types that have redundancy, that's your choice and data and your money and your time. You've got five bays and you can populate them as best suits you. If you think you might want to add redundancy to a storage pool at a later date then start a single drive SHR (with no drive protection). If you are sure you won't need it then a Basic storage pool will do.

So during the initial setup of DSM, even I have only one drive in the NAS, I can choose SHR? I read different stories. Some said that I need to have at least two drives in the NAS to use SHR but others said that I could do it with only one drive initially. Since I am not sure if I will need it, if possible, perhaps better to choose SHR than Basic?
 
If you only have one drive then you can still start a SHR pool. This is my storage pool 2 on the DS1520+. My storage pool 1 is a four drive SHR-1. I chose this setup so that I had options later to migrate to a four bay NAS if the chassis failed and funds were tight, or big drives got cheaper and four would be enough.

1683994755439.png


I rebuilt my DS215j with two Basic pools.
 
Redundancy has absolutely nothing to do with backup. Redundancy is for up time. Backup is backup, and it is always off-NAS. So one might infer that redundancy is not a substitute for backup. That would be a correct inference. Whether or not you choose redundancy, you should have a backup if your data is important.
 

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