Specifies the config of disk options for a group of VM instances.
.. attribute:: boot_disk_type
Optional. Type of the boot disk (default is “pd-standard”).
Valid values: “pd-ssd” (Persistent Disk Solid State Drive) or
“pd-standard” (Persistent Disk Hard Disk Drive).
Number of attached SSDs, from 0 to 4 (default is 0). If SSDs
are not attached, the boot disk is used to store runtime logs
and HDFS <https://hadoop.apache.org/docs/r1.2.1/hdfs_user_gui
de.html>__ data. If one or more SSDs are attached, this
runtime bulk data is spread across them, and the boot disk
contains only basic config and installed binaries.
