Storage pools/volumes and RAID type

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Storage pools/volumes and RAID type

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fairly new to the world of Synology NAS. I am about to take delivery of a DS920+ with 4 times 4TB. My question is about the storage pools/storage volumes.
I would like to pair the hard drives as follow: one pair for business and one pair for personal stuff (for each pair there is the main drive, while the other drive is used for backup).
Given my "idea" of setup,
- should I create one single RAID6 storage pool (and have 4 volumes - one for business, one for business's backup, one for personal stuff and the last one for backup of personal stuff)
- or is it wiser to create two RAID1 storage pools (each pool would have 2 volumes and hence one pool for business and one for personal).

I guess having multiple pools is less efficient as a single one (?) I am leaning towards the one-pool solution. However, given that I am fairly new to nas, does it make sense? or shall I go for another type of RAID?
Backup in the same enclosure is not backup just as RAID is not backup. So with that out of the way, if you are looking for a redundant scenario then maybe 2xRAID1 would be better and safe just because you will have logically separated volumes (2 storage pools with a single RAID1 volume).

Having multiple volumes in a single pool (like RAID6) would give you the same raw space and redundancy as 2xRAID1, so it's really up to you how you want to solve this. If you are going with a single larger pool with 2 drive redundancy you are again having the same raw space as 2xRAID1 but logically a single volume vs two.

From a "safe point" perspective (IMHO), running with 2xraid1 would be better, but do not consider RAID as a backup in any of the above scenarios. Especially if you will keep the "backup" drives in the same NAS.

Backup needs to be a copy of data on a separated device (hdd, nas, cloud etc) from your main source.
Welcome to the forum!

Just to add to @Rusty on RAID 1 and RAID 6. The default, unless you catch it during the initial system setup*, will be to make one storage pool from the installed drives based on SHR-1. Synology Hybrid RAID is similar to normal RAID but has some flexibility when using drives of different capacities. SHR-1 is SHR with one drive redundancy, like RAID 1 and RAID 5 and behaves like them when you have 2 drives (mirrored) or more. SHR-2 has two drive redundancy, like RAID 6.

I would assume most home users will be using SHR.

You can also deploy drives as Basic storage pools, where each one is separate and has no inherent resilience. So you could deploy four Basic pools, each with a separate volume. You would have then to manage backing up volume 1 to 2 and 3 to 4. But as already said, backing up within the same enclosure/NAS isn't really backup. If there's malware or error then all your storage is at risk. Better is to use external USB (disconnect when not needed), to another NAS (locally, but remote is better), and secure cloud storage. The optional Hyper Backup package is able to have multiple backup tasks to different destinations.

If you deploy two SHR-1 / RAID 1 then you can have two drives fail which would lead to either 0% data loss or 50%, depending on which two. But with three drive failures you would still have 50% data loss.

With one SHR-2 / RAID 6 the odds are different: two drives fail and you have 0% data loss, but with three failures it becomes 100%.

A final note, the DSM operating system is deployed on all drives in its own partition and allows for all but one drive to fail and the NAS still runs. But any additional package you install from Package Center will be installed (configuration files and database) on only one of the volumes you created (i.e. on of the storage pools). When you only have one volume you don't get a choice, it's volume1, but with more you have a setting to determine at time of package's installation where it is put. And Synology haven't made a simple way to move packages between volumes.

* I think there's a question about performance vs flexibility somewhere in setup screens. Here you need to actively say you want to do your own thing.
If you want to avoid making a SHR-1 with four drives then you could start setting up the NAS with two drives. This would default to SHR-1 making a mirrored array (like RAID 1). You can later add the other drives and within Storage Manager you can tell it to create a second storage pool, add them to the existing one, Or you can add to the existing one and also make it SHR-2 at the same time.

I'm using SHR and haven't had any problems. Only the very large [and expensive] NAS models don't support SHR so you are unlikely to have a problem later on.
Thx Fredbert. Does it mean that if I want to go for double SHR-1 I can't do it right away in the first setup? And so I would need first to install two drives set up a pool and volume for these two. And once complete I add two more drives and create a new pool/volume for these last two? I can't install the 4 drives and then create two SHR-1 pools/volumes "in one go"?
No that wasn't what I was saying

You can install all four drives at the start and then hope you don't miss the point in the installation where it asks how to setup the storage. The first time I did it I didn't realise quite what it was asking, nor the implications, and ended getting a default storage setup (that was on a two bay NAS so it was SHR-1, like RAID 1, if it was on a4/5 bay NAS it would be SHR-1 with all drives, like RAID 5). If nothing else I wanted to have a look at what else was possible but missed that. I made sure I was more careful the next time I did it.

I was just saying be careful not to miss that bit in the initial setup because you will have to restart the storage again if you get it wrong.
On initial setup I remember seeing an option when building the array or the pool (I cant remember which) and its asks if you want Speed or "something else" and I dont remember what the something else was... does anyone remember and what the differences are? or more importantly what the implications were?

I know when I setup my folders initially, I didnt understand the implications of enabling data integrity and data scrubbing, I wanted that, so I have to make new folders and move the files from folder1 to folder2 with data integrity enabled. The space reclamation process ensued.... but I didnt know.

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