I have a "x11 ready" 846b with the single sas3 expander backplane where I replaced the fans with the older fan models (6.3k rpm instead of the stock 11k rpm) and the psu with the 920 sq.
System and psu fans are audible, but not as annoying as the noise of the hdds seeking
Indeed!! I've been making a list of hardware that is useful for mounting spinning HDD's and reducing vibration.
Get some sort of ssd caching (cachecade, maxcache) to avoid as much as possible random small io.
You know, SSD caching or implementing a fast tier with SSD's is one of the most fascinating problems I'm working on right now. I'm not hugely enthusiastic about ZoL, Btrfs is more interesting, and I'm most interested in bcache, bcachefs, and LVM+XFS+dm_cache. Re: dm-cache I have a few SLC SAS3 HGST SSD's 100 GB and 200 GB, and I wonder whether these would be good for the fast part of the pair in dm-cache.
Actually, I've been thinking about creating an all-SSD filer (might be expensive, but remember, the "I" in "RAID" means "inexpensive"). In the background, it syncs with the backing filer that is implemented using large-capacity spinning SSD's.