I have a Cisco UCS 240M3 that hasn't been using in a couple years and I would really like to start utilizing this box since it has dual 10core CPUs with 128GB of RAM.

it has 24 2.5" drive bays. My question is: how many parity drives would I realistically need assuming I would be utilizing all 5TB 2.5" drives in each slot(minus the two slots I plan on using for Cache)? 

I'm completely new to UnRaid and just don't want to make any assumptions. Realistically, I'll only be filling 6-8 drive bays initially with 5TB drives and just two 1-2TB SSDs for caching. 

 

Unraid supports up to 2 parity drives (that allows you to lose up to 2 drives before things get really ugly).

Whether you use 0, 1 or 2 parity drives is really based on your tolerance for losing data. I use 2 parity drives because the outlay to have 2 is worth the security of being more likely to recover from a lost drive - to me.

With that drive count I would definitely recommend dual parity.

41 minutes ago, whipdancer said:

Unraid supports up to 2 parity drives (that allows you to lose up to 2 drives before things get really ugly).

Whether you use 0, 1 or 2 parity drives is really based on your tolerance for losing data. I use 2 parity drives because the outlay to have 2 is worth the security of being more likely to recover from a lost drive - to me.

Ah, understood. I still can't help but think in terms of a traditional RAID array and just really don't want to make any assumptions. I definitely plan on having two drives for parity, just wasn't sure I had say sixteen 5TB drives on this unit if I would need a certain number of drives to ensure fault tolerance. 
Thanks for the clarification, it is appreciated.

15 minutes ago, Phenix51 said:

if I would need a certain number of drives to ensure fault tolerance. 

The one key thing with unRaid vs "traditional RAID systems" is that on a traditional RAID, if you exceed your fault tolerance, you've lost everything, 100% gone, sorry about your luck.

 

unRaid, you will only ever lose a fraction under the same circumstances.  (Assuming of course that the cause of the fault wasn't that a stampede of wild elephants decided that your server room made a good place to have some fun in - in which case at least you have a good story to tell)