I have a server I'd like to use purely as a VM host. My preference would be to have no array and a couple of disks as a BTRFS cache, but when I try that I get: "no array disk devices have been assigned". I'm not hugely worried about data integrity at this point.

 

I'd like to use UnRAID for this task since the GPU passthrough and docker management stuff seem great so far.

 

EDIT: I've assigned my smallest disk to be data-only (don't plan to use it) and have a 2TB BTRFS raid. Decent enough workaround for now

unRAID is never intended to use that way. You will get constant warning / error that your parity is invalid.

It will not do any harm using unraid this way. There has to be one data disk so the array will start and therefore docker and vm manager start.

If you dont use a parity yes you will get warnings your data is not protected. But you will find that without a parity drive your write speeds will be quicker (same as cache) as there will be no parity writes.

 

However rather than use a btrfs cache and store your vms there, i would use xfs and probably use the drives in the array. If your drives are ssds then i would use them as xfs but unassigned drives outside the array.

Having a cache drive is of no advantage if you not using parity as write speeds will be the same.

Which warnings/errors are you guys talking about? I never used parity and  there are no warnings/errors.

The only difference is that you get an orange triangle instead of a green ball next to array started.

Which warnings/errors are you guys talking about? I never used parity and  there are no warnings/errors.

The only difference is that you get an orange triangle instead of a green ball next to array started.

 

I just assumed that  as under the array started where i see the green ball it also says Parity is valid. So i just assumed it would say Parity invalid without a parity drive. But to be honest i havent run without parity i shouldnt really have commented on that. My bad

Which warnings/errors are you guys talking about? I never used parity and  there are no warnings/errors.

The only difference is that you get an orange triangle instead of a green ball next to array started.

 

I just assumed that  as under the array started where i see the green ball it also says Parity is valid. So i just assumed it would say Parity invalid without a parity drive. But to be honest i havent run without parity i shouldnt really have commented on that. My bad

Yes, shame on you! 

I did not mean to sound angry/harsh if that is how it came out.

It did say Parity is invalid in my case. In fact, my weekly array status email constantly said there was a problem with my Parity until I finished the migration and added the Parity back.

However rather than use a btrfs cache and store your vms there, i would use xfs and probably use the drives in the array. If your drives are ssds then i would use them as xfs but unassigned drives outside the array.

Having a cache drive is of no advantage if you not using parity as write speeds will be the same.

 

If I understand correctly, you are recomending that I just build a standard multi-disk xfs array rather than a btrfs cache, only leave out parity. I would like to leave the option open to build out a larger array with parity at a later date - so I think my best bet is to stick with the btrfs cache for now? Shouldnt have too much effect short term while requiring leas copying of data long term.

It did say Parity is invalid in my case. In fact, my weekly array status email constantly said there was a problem with my Parity until I finished the migration and added the Parity back.

But then you have enabled something to get warnings 

Which warnings/errors are you guys talking about? I never used parity and  there are no warnings/errors.

The only difference is that you get an orange triangle instead of a green ball next to array started.

 

I just assumed that  as under the array started where i see the green ball it also says Parity is valid. So i just assumed it would say Parity invalid without a parity drive. But to be honest i havent run without parity i shouldnt really have commented on that. My bad

Yes, shame on you! 

I did not mean to sound angry/harsh if that is how it came out.

 

ha no didnt sound that way at all