I guess with fresh SAS drives I could get close to the physical limit of dual 4 GBit with the controller. However, that already requires me to make seperate RAID sets and thereby loosing 2 more disks on parity. Multipathing is supported in theory, but requires specific software I can't use in my enviroment.
Smart is supported, but some of the drives are so old that hey show a long list of relocated blocks already. Time to move on...
Best is to replace the entire chassis soon with some internal PCIe based SAS/SATA RAID6 controllers such as from Areca or similar and reduce the number of disks a bit.
As of now I tend to build a server with say 24 3.5" HDDs using Supermicro chassis with SAS backplanes. Those backplanes should be routed to external, then bridged to intern again and spread over two or thre RAID6 RAID controllers with external ports. That gives me option to grow the number of disks or RAID6 controllers as needed, or just reconnect to a second standby server in case of a malfunction on the server/mainboard. Another option would be to cluster (more complex) or to mirror (way more expensive, double disks & controllers).
For security I am going to use Undelete and Syncovery, in combination with constant defragmentation (which improves performance and helps in desaster recovery situations). This should be a very cost efficient and hopefully reliable solution.
I also looked into ZFS, but it was too slow and its caching is too limited from my perspective. After all, we do no rocket science here
