raid5/6

Hi so I just finished configuring my raid 5 that has 4 4tb drive and I was wondering what the best way to impliment a cache drive would be. If there is a good way what size would be enough? I tought of using a 128gb ssd to start with since what I usually transfer are media like movies series etc...

I have been using BTRFS RAID 1 for data and meta-data with two hard disk drives for a while now. This set up is on my network storage server. My desktops simply runs ext4 (not a fan of LVM yet). I am using two 1TB HDD totalling 1TB capacity (no surprises as using RAID 1); if I was to add...