How does unraid handle vm images larger than their original disk?

[wbsmolen]

I'm trialing unraid right now so pardon my ignorance. 

 

How exactly does unraid handle vm images that approach/break the total size of the disk I allocate the original VM on? Eg I have no issue provisioning a 2tb vm image on a 1tb physical disk in my array. What happens when that 2tb vm image hits 1tb? 

[Squid]

The vm will pause because it cant allocate any more physical space to the vdisk

[wbsmolen]

Does unraid support vm storage across multiple disk files?

[bastl]

6 hours ago, wbsmolen said:

Does unraid support vm storage across multiple disk files?

Each vdisk for the vm is a unique harddrive. For example you can add 3 1tb vdisks hosted on 3 different physical drives. VMs will recognise them as 3 individual drives. You can use software raid functions inside the VM, depending on the os to create a raid, if you like. Not tried it myself, but should be possible. 

 

But keep in mind, if you use vdisks you add a layer of emulation that uses ressources and might slow things down a bit. Better solution is to directly passthrough the 3 physical disks from my example.

[itimpi]

6 hours ago, wbsmolen said:

Does unraid support vm storage across multiple disk files?

If you mean splitting a single vdisk into multiple files so that it could be spread across multiple physical drives then is definitely not supported as a standard feature on Unraid.
 

I am not sure, however, if you created the vdisk on a different system (e.g. on VirtualBox or VMWare) and selected the option to split the vdisk into multiple files whether you could then move that file set to Unraid and then KVM on Unraid could be told somehow to use such a set operating as a single vdisk.  I must admit this is not something I have ever tried or even looked into.   It might be worth asking on KVM related forums as to whether KVM has such a capability in the first place as if it does then one could probably get it to work on Unraid with a bit of CLI work.

[wbsmolen]

On 3/15/2020 at 6:27 AM, itimpi said:

If you mean splitting a single vdisk into multiple files so that it could be spread across multiple physical drives then is definitely not supported as a standard feature on Unraid.
 

I am not sure, however, if you created the vdisk on a different system (e.g. on VirtualBox or VMWare) and selected the option to split the vdisk into multiple files whether you could then move that file set to Unraid and then KVM on Unraid could be told somehow to use such a set operating as a single vdisk.  I must admit this is not something I have ever tried or even looked into.   It might be worth asking on KVM related forums as to whether KVM has such a capability in the first place as if it does then one could probably get it to work on Unraid with a bit of CLI work.

FWIW -- this is what I was getting at. 

 

I added more cache storage and called it a day. I'm guessing kvm perf navigating multiple disk drivers across multiple physical drives would be suboptimal, if at all possible.