azure-ephemeral-disks.md

Using ephemeral storage within clusters deployed by Muchos for Azure

By default for Azure based clusters, Muchos will create 3 data disks, each of size 128GiB, attached to each VM. These managed disks provide persistent storage which ensures that the data in HDFS is safe and consistent even if the VMs are deallocated (stopped).

However, if you'd like to use only the ephemeral / temporary disk storage for HDFS, you first need to understand that using temp storage will result in lost data across VM deallocate - start cycles. If that behavior is acceptable for your dev/test scenario, there are two options available to use ephemeral storage within Azure:

• Use the temporary SSD disk which is available on most VM types. This tends to be smaller in size. Refer to the Azure VM sizes page for details on temp storage sizes
• Use the Lsv2 series VMs, Lasv3 series VMs or Lsv3 series VMs which offer larger amounts of NVME based temp storage

For using "regular" temporary storage (non-NVME), you need to change the following within the azure section within muchos.props:

• data_disk_count needs to be set to 0
• mount_root within the azure section needs to be set to `/mnt/resource'

If you'd like larger NVME temporary disks, another option is to use the storage-optimized Lsv2 VM type in Azure. To use the NVME disks available in these VMs, you must change the following within the azure section within muchos.props:

• vm_sku needs to be set to one of the sizes from this page, this page or this page, for example Standard_L8s_v2.
• data_disk_count needs to be set to 0
• mount_root within the azure section should be set to /var/data (which is also the default)
• azure_disk_device_path should be set to /dev
• azure_disk_device_pattern should be set to nvme*n1