I have a Silverstone DS380 8 bay case running 8 x 4TB drives using an old Intel i5 2500k based system and a firmware modded IBM M1015 disk controller. 7 of these drives are merged using UnionFS configured as data and content drives for SnapRaid with the 8th drive allocated as content and parity. Ideally I want more than one parity drive, however I also really need more storage space and I don't have the cash to replace the drives with something bigger. Everything is backed up to the cloud and currently I am deleting large files I don't have immediate need of to reclaim space (knowing I can restore from the cloud if need be).
I do have a couple of spare 4TB drives though and I was thinking I might get a basic 2 bay external hard drive enclosure in which I could put these drives into. I have no free expansion slots on the motherboard of my OMV box, so I'd have to attach this external enclosure via USB2. To maximise the data access performance I was thinking I'd add these two disks in the external enclosure as parity disks. Once fully synced I'd then reconfigure the internal parity disk to be part of the UnionFS and add it into SnapRaid as a data/content disk.
Does this sound like an ok plan given my situation? Are there any pitfalls of using external enclosures for parity disks?
I see USB is specifically called out as not recommended;
Not sure what option I have at present though. I'm the only user of this NAS, so provided the only impact of using USB is performance I think I'll just have to wear it. Ended up buying one of these as the seller had a refurb unit going cheap;