So I have read a ton of threads on ZFS in Unraid. I am switching from Truenas Scale I have been using ZFS on this for a while. In most of the posts on why not to go ZFS, it has to do with the cost of adding disks or power usage. If you took the cost out of the equation would you go ZFS? This machine will pretty much be only for Plex and the arr apps. The biggest reason I am leaning toward ZFS is Caching. I personally like the way ZFS does caching better. I will have 192GB of ECC RAM for ARC cache. I was going to run all apps off two NVMe drives in a mirrored ZFS pool. I was also going to have 2-4 Sata SSDs for L2ARC Cache. I was going to do x6 16TB drives in two Striped disk groups of RAIDz1. I know this will be overkill for plex but how I look at it is a HDD is terrible for IOP performance. the caching will load the file as it is read so as the user continues to watch the movie/show the whole thing will already be in the cache. This would take the load off the HDD so when I have multiple people watching at the same time there is less chance that I could have a high disk queue length. Let me know what you guys think

59 minutes ago, Zachhll said:

The biggest reason I am leaning toward ZFS is Caching. I personally like the way ZFS does caching better.

That rumor is in everybody's mouths, its simply wrong.

The famous "ARC-Cache" is stupid like a dog (old, blind and with 4 broken legs). It fills up quickly, stays much too long and does not clean up anytime.

 

So, after the few files you need to fill up the cache initially, you wont see any benefit.

 

I've once proposed a universal and hopefully better way to implement a working and adaptive read cache into unraid, but besides many people that "liked" it, there never was a response from limetech in the last 2 years now. Instead they brought out zfs now and have a hard time to get it up running and showing at least minor improvements. Its simply a flop.

 

By no means is it perfect for everything but for my use case I think it works well. I am currently doing this on truenas scale. Once a user starts watching something in plex it will cache the whole file that is being read. That way as the user is reading the file at 5MBs for 2 hours that whole file has already been moved to the cache. I don't expect a file that someone hasn't watched to be in cache most of the time. but the cache will make the HDD spend less time reading the file.