Using cache in Raid1 config as array

[EvolvedKiwi]

I've recently acquired a R730xd LFF and would like some advice on my plan for configuring the array.  My original plan was to use 2 x 1TB ssd's for the array but this isnt viable as i've read that Trim is not available due to the parity being mismatched between the drives after the Trim command is run.  I have 12 x 3.5in drives that i had planned to use for the pools while using the 2 x 2.5in bays at the back for the ssds for the array with no cache.  If i have to mess around using 2 of the 3.5in drives for the array that messes up my pool design.

 

My question(s) is:

• can i set a USB dive as my array drive with no parity drive and then create a mirrored cache while setting all folders to run off the cache directly with no Move being carried out back to the array? 
  • If this is possible, what problems am i likely to encounter with such a configuration? 

 

Im unsure if the cache needs to be btrfs or xfs given btrfs supports discard=async mount option while xfs needs to be manually trimmed (i think!).

 

Any help would be appreciated, thank you.

[Kilrah]

26 minutes ago, EvolvedKiwi said:

can i set a USB dive as my array drive with no parity drive and then create a mirrored cache while setting all folders to run off the cache directly with no Move being carried out back to the array?

Yes that's fine.

 

26 minutes ago, EvolvedKiwi said:

Im unsure if the cache needs to be btrfs or xfs

XFS only supports single drive so has to be btrfs or zfs.

[itimpi]

You need to distinguish between 'pool' which is a a group of one or more disks that are not part of the main array and 'cache' which is functionality associated with a share (although there is confusion about the fact that for historical reasons people often have a pool called 'cache'), and you can have multiple pools.   If you only set up 'primary' storage for a share then there is no caching involved and you can specify whether that primary storage is a pool or the main array.    In the scenario you describe above then the primary storage would be the pool you specify and all files for such shares would be on that pool.  Many new uses are now going that route.   In the future we expect the need to have a dummy usb drive in the Unraid type array will be removed.

 

A multi-drive pool has to be either btrfs or zfs.   You can only use xfs on a single drive pool.

[EvolvedKiwi]

45 minutes ago, itimpi said:

You need to distinguish between 'pool' which is a a group of one or more disks that are not part of the main array and 'cache' which is functionality associated with a share (although there is confusion about the fact that for historical reasons people often have a pool called 'cache'), and you can have multiple pools.   If you only set up 'primary' storage for a share then there is no caching involved and you can specify whether that primary storage is a pool or the main array.

Apologies for the confusion, mixing terminologies up is something im golden at.

 

The 'cache' is indeed a pool defined with SSD's instead of spinning disk for that performance bump with the docker and vm usage i have planned.

 

47 minutes ago, itimpi said:

A multi-drive pool has to be either btrfs or zfs.   You can only use xfs on a single drive pool.

Thank you for the clarification on that, also thank you @Kilrah for your response also.