Upgrade RAID-5 HDs with SSD Cache

[kicks66]

I've recently installed a set of 8x12TB hard drives into a RAID-5 configuration. I am looking to take advantage of the SSD cache acceleration feature, and was wondering how many SSDs I need to do this? Do I install 2x SSDs to get advantage to this? And does that mean space will be (6x12TB - (1x12TB)) + (2x SSD size)? Or is it a different calculation? Is there an issue with having 6x 12TB drives and then smaller SSD drives in RAID-5 + SSD acceleration setup?

[storageman]

Eek! 8 x 12TB a bit risky with RAID 5. RAID 6 safer, think of the rebuild times on 12TB drives!
Read/write SSD cache drives do not add to the pool size, whereas Qtier (tiering) additional SSDs does.

[kicks66]

Storageman - we currently have a remote replica of the last 42TB of data to another RAID-5 NAS, and all data backed up to Google Drive on an unlimited storage plan and a 1Gbps internet connection. Do you think it's worth doing a RAID-6 on top of that?

So if I was to add the SSD cache, would I be able to add just one (say 2TB SSD) drive and get the benefit from it? And the others would form a RAID-5 with 7x 12TB drives?

[storageman]

Storageman - we currently have a remote replica of the last 42TB of data to another RAID-5 NAS, and all data backed up to Google Drive on an unlimited storage plan and a 1Gbps internet connection. Do you think it's worth doing a RAID-6 on top of that?

So if I was to add the SSD cache, would I be able to add just one (say 2TB SSD) drive and get the benefit from it? And the others would form a RAID-5 with 7x 12TB drives?

It's your decision, recovering 40TB+ would still be a pain!
1xSSD = read cache
2xSSD= read/write cache

But what you using it for, would it benefit from caching?

If it's largely sequential work SSD don't add much, whereas tiering improves both random and sequential work (but you need minimum 2 SSDs for Qtier or the entire pool might fail).
What is the NAS model?