What is the node storage class –NVME/SSD?

The default storage in one of your VMs is a virtual block device attached to the VM and mapped to the VM’s host’s local disk. The host’s local physical disk is an SSD (i.e. not an NVMe drive).  The performance of these virtual block devices is a bit difficult to assess because the virtualization is optimizing a lot of things for you.

Some things that will affect the performance of your local disk:

• The VM’s operating system will cache files in memory using any free memory allocated to your VM.  Repeatedly accessing any file that is smaller than your VM’s free memory will likely be very fast because it will only read/write to memory. You can explicitly skip this cache.  For example, if you use the dd command you can add oflag=direct and it will skip this cache.
• The host’s hypervisor uses any free physical memory to cache any virtual disk blocks used by the VMs that it is hosting.  Repeatedly accessing the same block of a disk in a VM will likely be very fast because it will only use blocks that the host hypervisor is caching in its memory.  This cache is shared by all VMs on that host and the availability of this cache depends on the way other VMs are using their disk blocks. There is no way for a user to choose to skip this cache.
• The physical disk is an SSD.  Even if you manage to write to the physical disk, it should be faster than if you were using a spinning disk.
• Currently, most hosts on FABRIC have a couple hundred Gigs of memory and are underutilized.  In most cases, accessing a local disk will only result in memory reads/writes.  This may  change as the testbed utilization increases.

If you want to use an NVMe drive you need to add an NVMe drive component to your VM (like how you add an NIC component).   Checkout the NVMe examples listed the in the “start here” Jupyter example notebook.

Paul