Been reading up on SnapRAID and that sounds like an good idea for what I need. Based in Ireland so thankfully power cuts aren't an issue. Can I use SnapRAID in conjunction with OMV?
https://www.scan.co.uk/product…o-usb-30-esata-host-ports
Could I use it with this have a few HDD's in this and hook it up to my Pi4 and have it all set up as a media server?
Thanks for all the advice so far 
Ok so the reason I want Raid 5 is I want some sense of recovery so if a hard drive decided to stop working I dont loose almost 3TB of data which I will somehow have to manage to get back. But at the same time I dont want to loose half of my storage to 1 to 1 backups. So from what I've read about Raid 5 in will loose 1 drive to parity data. And yes the whole 3 smaller and 2 larger drives I know with a Raid setup they will only use the smallest drives as a base. The 2 extra 4TB drives are extra ones I have and I'd rather loose out on 2TB of data then having to go out and buy 3 x 4TB drives.
TerraMaster D5-300 USB3.0(5Gbps) Type C 5-Bay External Hard Drive RAID Enclosure Support RAID 5 Hard Drive RAID Storage (Up to 70TB, Diskless) https://smile.amazon.com/dp/B0…_r_cp_apa_i_UIDZDbEH43WWN
That is the 5 bay DAS I am looking at.
Ok so just recently joined and looking for some help and will appreciate any advice. I recently bought a Raspberry Pi4 4gb and want to set it up with Open Media Vault and want redundancy. I want to hook up a 5 bay DAS to it and was wondering should I go for a DAS with Raid 5 integrated into it or should I go with a cheaper option without Raid 5 integrated and use software based Raid 5 in OMV? I also possibly somewhere down the line would like to attach another DAS in a Raid 1 configuration to use as backup for more important things that I could keep locally instead of relying on cloud based services. The Raid 5 drives would be 3 x 3TB and 2 x 4TB. The Raid 1 drives would be 2 x 2TB but would be older then the other drives but not bought/used the same amount so hopefully both wouldn't fail at the same time. Thanks for any info
