Hey Guys,

 

So here is what i know about the cache pool. Its by default using btrfs (i dont know much about this) and uses something similar to raid 1 (mirror). The unRaid cache pool accepts multiple drives (im unsure if there is a limit). So i have few questions regarding this.

 

i have couple of SSDs sitting around and couple of spinny disks as well. And im hoping to use as many as i can as my cache to maximise the speeds and capacity of my cache pool (as the unRaid main data pool is far too slow for normal writes). Anyway, for sake or argument, lets say i have 2x 240gb SSDs and 2x 1tb Spinny Drives (WD Blues).

 

1. Given the above drives, is it wise for me to add all 4 drives into the cache pool, or should i only add either the 2 ssds or the 2 spinny drives?

2. If its fine to add all 4 drives to the cache pool, then what sort of capacity would i get as a result for the cache?

3. If its fine to add all 4 drives to the cache pool, then what sort of SPEEDs would i expect from the cache pool? (lets say individually the SSDs can do 500MB/s and spinny drives can do 100MB/s).

 

Thats all for now,

 

Thanks in advance

1. Given the above drives, is it wise for me to add all 4 drives into the cache pool, or should i only add either the 2 ssds or the 2 spinny drives?

Use the 2 SSDs or the 2 HDDs

 

2. If its fine to add all 4 drives to the cache pool, then what sort of capacity would i get as a result for the cache?

http://carfax.org.uk/btrfs-usage/

 

3. If its fine to add all 4 drives to the cache pool, then what sort of SPEEDs would i expect from the cache pool? (lets say individually the SSDs can do 500MB/s and spinny drives can do 100MB/s).

 

SSD speed when the data you're reading is on one of the SSDs (SSD speed when writing only if by chance both are being used by the two copies), HDD speed when the data is one one of the HDDs, no way of knowing where the data will go when writing.

 

 

Hmm, its a little annoying that i have to choose between either 2 ssds or 2 hdds.

 

Out of curiosity, what if i chose to have 2 ssds with slightly different capacity and slightly different sizes. Lets say 450MB/s vs 500MB/s and 240GB vs 250GB. Would that cause any issues?

No issues, usable size would be 240GB.