Does multi storage pools make sense to avoid more damage from a bad disk?

Question

I am a beginner of NAS(and its hardwares), and I get some basic knowledge about RAID from Synology's guidebook. There are many tutorials taught me how to use my hard drive devices to create the storage pool. But I'm not sure about the sense of creating multi pools with different RAID array mode.

My devices:

• 6 bays DS918+ DIY NAS. No extra bays.
• 6 * 8TB HHD, and I installed Synology DSM7.1 on one of them. The storage space is more than enough so I will never buy more bigger or smaller disks. If any of the 6 ones is damaged, I just want to buy a same one to replace.

My demands:

1. Store videos, less than 20TB. There will be infrequent write operations, that means I will save movies, and watch them again and again in weekends. I don' t care about speed, but often worry about how troublesome it will be when any disk dead. It is ok for me to download some of the movies again, but I don' t want to lose all of them at the same time.
2. Store photos and documents and snapshots, less than 4TB. This is usually considered as "important files", so I have already save copies in my PC, mobile HDD and cloud storage before I start using NAS.

Considering these two demands, I can accept the loss of some data when a disk damaged, but want to make sure it won' t break other disks and cause more damage.

As far as i understand(of course could be completely wrong), Basic, RAID1, or RAID5 might come in handy for my demands. But there is a saying that another disk may damage too after the first disk dead when rebuilding RAID5.

What really confused me is that, will it be better for me to create a storage pool for demand1 and another pool for demand2, comparing with an only pool for two demands together? If so, or not, which array mode is suitable for my requirement?

I wrote this question with the help of Google translate so welcome to edit if there are incorrect terms.

Answer 1

From my point of view the best you can do is to create one pool with RAID6. Such array can survive failure of two disks. The available space will be 4*8 ~ 32TB. If you want to go crazy and can get your information in 24TB you can create above RAID6 with one spare disk. This will give you more time to react on failed disk.

Of course the performance will be lower than RAID5 or RAID1 but you should balance the speed and safety.

Answer 2

This is bordering on opinion based (and off-topic here but)

• Avoid RAID5 on 8tb disks. There is some controversy but generally accepted wisdom is it should not be used on disks greater then 2tb.

• Be aware that RAID is not backup. It prevents data loss in case if disk failure, but not accudental deletion, filesystem corruption, theft etc.

• Consider using a single RAID6 setup for all your data. This will be simple to set up, gives you 32 tb of data and allows for up to 2 simultaneous disk failures.

This will give you better flexibility then RAID1 as well as more usable disk space and ease of use.

There may be other options (like SHR-2 and RAID10) but I would keep it simple and standards based here.