Configuring disks for a cloud server

When you create a cloud server, it is provisioned on a physical server in a RAID 10 configuration. This configuration provides a level of underlying redundancy without requiring you to invest extra configuration effort.

Persistent and ephemeral disks

The type and number of disks presented to a flavor can vary from class to class. Local disks can be persistent, or a mix of persistent and ephemeral. Both kinds of disks are protected from failure of the underlying hardware by RAID 10. If a server fails, the data on its ephemeral disk persists.

Persistent disks persist through user-initiated actions against a server; ephemeral disks do not. For example, if a snapshot action is initiated against a cloud server, it copies the persistent disk, but any data on an ephemeral disk is not copied.

Depending on the interface used, persistent and ephemeral disks are labeled differently:

  • The Cloud Servers API labels the persistent disk as Disk and the ephemeral disk as Ephemeral.

  • The Cloud Control Panel labels the persistent disk as System Disk and the ephemeral disks as Data Disk.

Presentation of disks to the operating system

A flavor may have zero or multiple individual disks presented to it. Additional disks are supplied unformatted and without a partition. Some behavior varies with the operating system:

  • Linux labels the system disk /dev/xvda. Subsequent disks are labeled starting at /dev/xvde and proceeding through the alphabet for each additional local disk or attached Cloud Block Storage volume.

  • Windows requires that the disk is brought online, a drive letter is assigned to it, and the disk is formatted.

Manual and automated disk configuration

Linux PVHVM images use cloud-init to format and expand the system disk’s root partition to fill the entire available drive space at boot. All other Linux images use the additional Disk Configuration setting to control this behavior:

  • Auto: The additional drive space is formatted and the root partition is expanded to fill the entire system disk. This is the default option.

  • Manual: The root partition is left unchanged and any additional space on the system disk is left unformatted and un-partitioned.

The manual setting results in a faster boot time for the server, because formatting adds additional time to the boot process. It also allows a higher degree of customization of the disk.

This option is not available for Windows.