btrfs cache pool - jbod / storage array style cache pool

[scorcho99]

I gather by default at least multiple disks in the cache pool go together as a btrfs raid 1 (btrfs style raid 1 anyway) disk. I've seen its possible to convert this to a striped disk as well.

 

Another idea was presented in the linked thread of having the cache pool disks be in a single disk / jbod mode instead. Basically, it would be like the unraid storage array only without parity protection. Did this ever get implemented? And if so how could I set it up?

 

 

[JorgeB]

2 minutes ago, scorcho99 said:

I've seen its possible to convert this to a striped disk as well.

 

It is.

 

3 minutes ago, scorcho99 said:

Basically, it would be like the unraid storage array only without parity protection. Did this ever get implemented? And if so how could I set it up?

 

You need to have at least one data disk assigned (it can even be a flash drive), then you can do what you want with the pool.

[scorcho99]

2 minutes ago, johnnie.black said:

You need to have at least one data disk assigned (it can even be a flash drive), then you can do what you want with the pool.

 

Great! Just to be clear, I also want a parity protected storage array. But I'd also like the two additional cache disks to have user shares extended across them. Basically, I want to store vms on the cache share but be able to move them from a ssd to a hdd or back in the cache pool without updating the VMs drive location.

 

[JorgeB]

Just now, scorcho99 said:

I want to store vms on the cache share but be able to move them from a ssd to a hdd or back in the cache pool without updating the VMs drive location.

 

You can do that by changing that share from use cache "prefer" to "yes" back and forth and running the mover (VMs will need to be shutdown to be moved).

[scorcho99]

2 minutes ago, johnnie.black said:

 

You can do that by changing that share from use cache "prefer" to "yes" back and forth and running the mover (VMs will need to be shutdown to be moved).

 

Huh, I thought the mover would move them to the main storage array.

 

I'll play around with it tonight but how do I set the cache pool up for single disks? I was under the impression it just does a btrfs mirror array by default. I've seen command line directions for changing the array type to striped but not to separate disks.

[JorgeB]

7 minutes ago, scorcho99 said:

I was under the impression it just does a btrfs mirror array by default. I've seen command line directions for changing the array type to striped but not to separate disks.

 

You can't use separate disks, you can use a single disk or a pool, if it's a pool it can be jbod, raid0/1/10 (also raid 5/6 but not recommended)

[scorcho99]

From reading around on btrfs it looks like there is a "single" raid mode that concatenate the disks together to get their total size even if the disks are a different size. Regular striping is more performant but it will lose space with mismatches sizes. That's nice. But as best as I can tell that will still be a single giant volume in the end, which isn't exactly what I'm looking for. With no way to control which physical disk the data is going on this isn't of great use to me.

 

I could use the single mode to glue a couple of my smaller ssds together and still get snapshots I guess.

[JorgeB]

Yes, that's the single profile: