Ephemeral disks are temporary storage devices that are often used for short-term data storage. These disks may not show up in the df -h output even though they appear in lsblk, this can be due to missing configuration that needs to be part of the startup script to automatically detect the number of ephemeral disks and create an ext4 file system mounted at the /nvme path. If multiple ephemeral disks are found, the script will create a RAID0 array of the disks for additional performance benefits, mounted at the /raid0 path.

Symptoms

When performing lsblk command, output:

When performing df -h command, output:

Prerequisites

• Applicable to instance types that support ephemeral disks.

Solution

Create a new instance with the below startup script:

#!/bin/bash

apt update && apt install -y nvme-cli mdadm

num_nvme=`nvme list | grep -i /dev | wc -l`

if [[ $num_nvme -eq 1 ]]; then
   dev_name=`nvme list | grep -i /dev | awk '{print $1}'`
   mkfs.ext4 $dev_name
   mkdir /nvme && mount -t ext4 /dev/nvme0n1 /nvme
elif [[ $num_nvme -gt 1 ]]; then
   dev_name=`nvme list | grep -i /dev | awk '{print $1}'`
   mdadm --create --verbose /dev/md127 --level=0 --raid-devices=$num_nvme $dev_name
   mkfs.ext4 /dev/md127
   mkdir /raid0 && mount -t ext4 /dev/md127 /raid0
else
   echo "no ephemeral drives detected"
fi

Verify

When a new instance is created, SSH into the VM and perform the below commands to verify disk attachment.

• lsblk

• df -h

This would show the ephemeral disks associated to the VM. If the issue persist perform the below:

confirm if the /raid0 directory exists and try remounting the file system with

# sudo mount -t ext4 /dev/md127 /raid0

Lastly, try df -h to confirm the change. 

If the issue persists, please contact Crusoe Support at support@crusoecloud.com and we will be happy to assist!

Additional Resources

• Formatting and Mounting Ephemeral Disks