SSD and HDD as Cache

[Hairy]

Hello

I have searched some information about that topic, but I am not 100% certain if this is even possible in Unraid and if there would be a benefit even.

Is there a way, to set a RAID1 TWO SSDs and one HDD of the same size?
And in addition, would there be a benefit of the speed of the SSD (be it only on the reading part) or is the speed determined by the general slowest device, in this case the HDD?

 

I read that some hardware RAID1 can be "smart" enought so that they primarly use the SSD RAID1 at first especial with the reading part, this seems to be called "write first", but is that method also implemented in the software RAID1 wich Unraid is using?

 

I know, it sounds a little ridiculous, but I am on to installing a Cache in my Unraid server, but I still don't trust consumer SSD's with 24/7 useage and my idea would be, to be on the safe side, that the HDD is like a "Backup/failsafe" of that. My goal would be, that the 12 "big disks" are only being used if needed, and Docker/VMs should be stored soley on the SSD's and on that small HDD.

Maybe the HDD as "hot spare" is also enough? So that if an SSD is going to die, that THEN the HDD will be utilized as failsafe, or am I too overthinking/scared of an failure  ? The question then would be, is there an automatic hot spare function? I thought I read it somewhere a year ago, but I cant find anything about it anymore besides that post: 

Would be interested what your thoughts are about that, or if it's completly nonesense what I am talking about.

 

[JorgeB]

17 minutes ago, Hairy said:

Is there a way, to set a RAID1 TWO SSDs and one HDD of the same size?

Yes.

 

17 minutes ago, Hairy said:

And in addition, would there be a benefit of the speed of the SSD

No.

 

 

[JorgeB]

Just now, JorgeB said:

No.

To expand, there would be some times when writes would go to both SSDs, others were it would go to one SSD and the HDD, it would alternate every new chunk, and when the HDD is used it would always be limited by the HDD speed.

[Hairy]

Ah got it, so it's not considering if the attached drives are SSD or HDD.
Oke, then the question which would be left is, is there a hot spare functionality without scripting it myself  ?

[JorgeB]

19 minutes ago, Hairy said:

is there a hot spare functionality without scripting it myself  ?

Nope.