Hybrid 4TB drive with SSD cache - parity or array?

[sneakybifta]

Hi,

 

I'm building my first unraid box and re purposing a couple of hard drives. For now, I have a standard 4TB drive and a hybrid Seagate 4TB/8GB ssd hybrid drive, and may add more drives to the array in future.

 

I've done some searching and understand I'm unlikely to see any performance benefit from the hybrid drive, but I can't work out whether it would be best as the parity drive or as the array drive. I don't really understand enough about how unraid works, I would imagine there's not much difference either way but should I be concerned about lots of writes knackering the SSD as parity or array?

 

The main purpose of this box is a Plex server

[c3]

Over time, the parity drive is given more writes than any other drive. If your array is 3 drives, D1, D2, and P1. When a file is written to D1, P1 gets writes too. And when a file is written to D2, P1 also gets writes. If you fill D1 with 2TB, and then fill D2 with 2TB (unRAID default behavior), P1 will have written 4TB, the same 2TB written twice.

 

The flash usage in the hybrid is optimized towards reads to boost boot and application load performance, and avoid the issues with overwrites. Most unRAID user reads are serviced by data drives. Only in a degraded state is the parity drive used for user reads.

 

Combined, the questionable best position would be a data drive.