Should I have separate RAID/Volume on Synology Expansion unit? What if it disconnects?

Hey There, I’m Danny. I followed your insights on videos when purchasing my upgrade to my original single bay Synology device. I have used a 920+ with 4 – 6TB WD Red Pro Drives and have had pretty good luck. I have the need to expand my storage and have purchased a DSX517 expansion unit with 5 – Seagate Iron Something or another 8TB NAS drives to add to the unit. I currently have the SHR configuration for RAID enabled on my single Volume on the 920. I also have two 250gb Samsung EVO 970 drives being used as read only cache in raid 0. I did try the read/write configuration but went to the read only configuration as my NAS primarily acts as a digital content library with limited Docker/VM use. I was wondering how I should proceed with expanding my storage pool. I have some enterprise storage experience, but primarily worked on the application layer. I have two questions and feel free to provide any other suggestions as you know your stuff. #1: Should I create an additional volume for the new expansion unit’s drives and convert from a single volume storage pool to multi? I have read concerns about spanning across the units in both forums and the enterprise but I wanted to get your insight on if my plan to go forward makes sense. I also wanted to ask your opinion on if I should dismount the two nvm ssd cache drives and mount a single 250gb drive on each volume for cache? Keep it in the read only config on the current volume? The current volume has 18TB usable and the new volume would potentially be much larger and wondered if I should move both ssd to the new larger volume. Any tips or direction is greatly appreciated. Keep up with the videos, I enjoy them!


It depends on your needs. If you want to maximize storage (price per TB) then it makes sense to have only one RAID across all drives. But there are concerns if cable breaks or connection got problems, you would have 5 drives disconnected and therefore very high chance to destroy your RAID and volume. People have managed to mount these drives back, but there is a risk. If you have a good backup in place this is an option to save money. Otherwise, it is better to have separate RAID and volume.
SSD cache when split will allow only READ operations. So, if another volume is not used for things like VMs or databases, then better to leave the cache where it is actually needed.

I hope this helps.

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